Hybrid servo pattern configurations for magnetic tape

ABSTRACT

A tape drive-implemented method, according to one embodiment, includes: using information read from one or more servo bands on a magnetic tape to position a magnetic tape head relative to the magnetic tape. An array of data transducers is positioned along the magnetic tape head, the array extending perpendicular to a direction of travel of the magnetic tape. Moreover, a group of servo readers is positioned at each end of the array of data transducers. A distance between each of the immediately adjacent servo readers in each of the groups of servo readers is less than or equal to one third of a prespecified width of each of the servo bands. Furthermore, the distance between each of the servo readers in each of the groups and the prespecified width are both measured in a direction perpendicular to the direction of travel of the magnetic tape.

BACKGROUND

The present invention relates to tape storage systems, and morespecifically, to hybrid servo pattern configurations for use withmagnetic tape recording systems and products.

Timing-based servo (TBS) is a technology which was developed for lineartape drives in the late 1990s. In TBS systems, recorded servo patternsinclude transitions with two different azimuthal slopes, thereby forminga chevron-type pattern. These patterned transitions allow for anestimate of the head lateral position to be determined by evaluating therelative timing of pulses generated by a servo reader reading thepatterns as they are passed over the servo reader.

In a TBS format, the servo pattern is prerecorded in several bandsdistributed across the tape. Typically, five or nine servo pattern bandsare included on a given tape which runs about parallel to a longitudinalaxis of the tape. Data is recorded in the regions of tape locatedbetween pairs of the servo bands. In read/write heads of IBM lineartape-open (LTO) and Enterprise tape drives, two servo readers arenormally available per head module, from which longitudinal position(LPOS) information as well as a position error signal (PES) may bederived. Effective detection of the TBS patterns is achieved by asynchronous servo channel employing a matched-filterinterpolator/correlator, which ensures desirable filtering of the servoreader signal.

Although TBS patterns have historically been able to provide sufficientpositioning data while reading from and/or writing to magnetic tape,conventional products have begun to experience setbacks in performanceefficiency. Specifically, as track densities continue to increase fortape media and tape drives, accurately controlling the lateral positionof a magnetic head and/or skew of the magnetic head with respect to tapeby using feedback generated by reading the TBS patterns has becomeincreasingly difficult. In fact, conventional servo basedimplementations may not be sufficiently accurate to ensure adequatepositioning of the data readers and writers that move along data tracksof magnetic tape having a sufficiently high track density. Furthermore,the repetition rate of the head lateral position estimates may be toolow to ensure proper track-following operation, as tape velocity variesduring use. The repetition rate of the head lateral position estimatesmay additionally be unable to support future actuators with largerbandwidths. It is also important to monitor tape dimensional stability(TDS), particularly as track density and tape capacity continue toincrease.

However, in the past tape skew and TDS measurements have been determinedfrom the information from servo bands on both sides of a head module, orinformation from servo readers on multiple head modules. In other words,to compute skew and/or TDS, conventional products have needed to obtainvalid servo information from more than one servo band and/or more thanone head module. This makes such conventional head modules particularlysusceptible to degraded performance and/or being rendered completelyuseless by servo defects, scratches caused by asperities on the surfaceof the magnetic tape, etc.

Some products have implemented servo bands having a hybrid servo patternin an attempt to alleviate some of the foregoing shortcomings. Hybridservo patterns employ a high density (HD) servo pattern in addition tothe TBS pattern, thereby providing some additional information. However,products implementing hybrid servo patterns have been unable to achievefunctionality while also enabling backward compatibility in a singletape drive. Backward compatibility is highly desirable for removablestorage media such as magnetic tape. For instance, backwardcompatibility allows a given tape drive to support multiple differentgenerations of magnetic tape. Accordingly, backward compatibility allowsusers to maximize flexibility of tape media resource arrangementsavailable to them.

To achieve backward compatibility among multiple generations of magnetictape, it is desirable that a number of data bands relative to servobands maintain a standard ratio while the data capacity of magnetictapes increase. Moreover, it is desirable that servo readers on a singlehead module are compatible with various different servo band formats.However, this has served as a significant issue for conventionalproducts thus far. Accordingly, achieving a magnetic tape and/or systemwhich is able to continue to increase data capacity, while alsoimproving data track following performance, as well as maintaining astandard ratio of data bands relative to servo bands is greatly desired.

SUMMARY

A tape drive-implemented method, according to one embodiment, includes:using information read by one or more servo readers from one or moreservo bands on a magnetic tape to position a magnetic tape head relativeto the magnetic tape. An array of data transducers is positioned alongthe magnetic tape head, the array extending perpendicular to a directionof travel of the magnetic tape. Moreover, a group of servo readers ispositioned at each end of the array of data transducers. A distancebetween each of the immediately adjacent servo readers in each of thegroups of servo readers is less than or equal to one third of aprespecified width of each of the servo bands. Furthermore, the distancebetween each of the servo readers in each of the groups and theprespecified width are both measured in a direction perpendicular to thedirection of travel of the magnetic tape.

A computer program product for positioning a magnetic head, according toone embodiment, includes a computer readable storage medium havingprogram instructions embodied therewith, wherein the computer readablestorage medium is not a transitory signal per se, the programinstructions executable by a tape drive to cause the tape drive toperform the foregoing method.

A tape cartridge, according to another embodiment, includes: a supplyreel and a magnetic tape having a plurality of servo bands. Each of theservo bands includes a high density servo pattern and two timing basedservo patterns, a longitudinal axis of each of the two timing basedservo patterns being oriented parallel to a longitudinal axis of thehigh density servo pattern. A combined width of the high density servopattern and one of the two timing based servo patterns in a given servoband is less than or equal to two thirds of a prespecified width of eachof the servo bands. Moreover, the combined width and the prespecifiedwidth are each measured in a direction perpendicular to a longitudinalaxis of the magnetic tape.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representational view of a network storage system, accordingto one embodiment.

FIG. 2 is a simplified view of a tape drive in a tape-based data storagesystem, according to one embodiment.

FIG. 3 is a representational view of a magnetic tape layout, accordingto one embodiment.

FIG. 4A is a partial representational view of a hybrid servo patternwritten in a dedicated area of a magnetic tape medium, according to oneembodiment.

FIG. 4B is a partial detailed view of a TBS pattern, according to oneembodiment.

FIG. 5A is a partial detailed view of a HD pattern, according to oneembodiment.

FIG. 5B is a graph plotting readback energy vs. frequency for the readerin FIG. 5A.

FIG. 5C is a partial detailed view of a HD pattern, according to oneembodiment.

FIG. 5D is a graph plotting readback energy vs. frequency for the readerin FIG. 5C.

FIG. 6 is a block diagram of a detector for HD patterns, according tothe prior art.

FIG. 7 is a block diagram of a detector for HD patterns, according toone embodiment.

FIG. 8A is a partial representational view of a conventional servo band.

FIG. 8B is a partial representational view of a conventional head modulepositioned over the conventional servo band of FIG. 8A.

FIG. 9A is a partial representational view of a magnetic tape andmagnetic tape head, according to one embodiment.

FIG. 9B is a partial detailed view of the portion of the magnetic tapeof FIG. 9A inside the dashed box labeled FIG. 9B, according to oneembodiment.

FIG. 9C is a partial detailed view of a data band of the magnetic tapeof FIG. 9A inside the dashed box labeled FIGS. 9C-9F, according to oneapproach.

FIG. 9D is a partial detailed view of a data band of the magnetic tapeof FIG. 9A inside the dashed box labeled FIGS. 9C-9F, according to oneapproach.

FIG. 9E is a partial detailed view of a data band of the magnetic tapeof FIG. 9A inside the dashed box labeled FIGS. 9C-9F, according to oneapproach.

FIG. 9F is a partial detailed view of a data band of the magnetic tapeof FIG. 9A inside the dashed box labeled FIGS. 9C-9F, according to oneapproach.

FIG. 9G is a partial detailed view of a portion of the magnetic tapehead of FIG. 9A inside the dashed box labeled FIGS. 9G-9H, according toone approach.

FIG. 9H is a partial detailed view of a portion of the magnetic tapehead of FIG. 9A inside the dashed box labeled FIGS. 9G-9H, according toone approach.

FIG. 10 is a flowchart of a method, according to one embodiment.

FIG. 11A is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 11B is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 11C is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 12A is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 12B is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 12C is a flowchart of sub-processes of the method of FIG. 10,according to one approach.

FIG. 13A is a simplified view of a magnetic tape and magnetic tape head,according to one embodiment.

FIG. 13B is a partial detailed view of a portion of the magnetic tapehead and magnetic tape of FIG. 13A inside the dashed box labeled FIG.13B, according to one approach.

FIG. 13C is a graph plotting servo signal vs. time, according to oneembodiment.

FIG. 13D is a graph plotting servo signal vs. time, according to oneembodiment.

FIG. 14A is a simplified view of a magnetic tape and magnetic tape head,according to one embodiment.

FIG. 14B is a partial detailed view of a portion of the magnetic tapehead and magnetic tape of FIG. 14A inside the dashed box labeled FIG.14B, according to one approach.

FIG. 14C is a graph plotting servo signal vs. time, according to oneembodiment.

FIG. 14D is a graph plotting servo signal vs. time, according to oneembodiment.

FIG. 15 is a perspective view of a data storage cartridge having acutaway portion, according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof for improving both magnetic tape recording systems and magnetictape products. The number and relative spacing between the servopatterns in the various approaches described herein, as well as thenumber and relative spacing between servo readers in the variousapproaches described herein allow for a corresponding magnetic tape headand tape drive to achieve improved performance while also enablingbackward compatibility for various styles (e.g., generations) ofmagnetic tape. As a result, by implementing various ones of thefollowing technical features, the shortcomings experienced inconventional magnetic tape products and conventional tape drives areovercome.

In one general embodiment, a tape drive-implemented method includes:determining a servo band configuration of servo bands on a magnetictape, using servo readers on a magnetic tape head to read one or more ofthe servo bands based on the determined servo band configuration, andusing information read from the one or more of the servo bands toposition the magnetic tape head relative to the magnetic tape. An arrayof data transducers is positioned along the magnetic tape head, thearray extending perpendicular to a direction of travel of the magnetictape. Moreover, a group of the servo readers is positioned at each endof the array of data transducers, and a distance between each of theimmediately adjacent servo readers in each of the groups of servoreaders is less than or equal to one third of a prespecified width ofeach of the servo bands. The distance between each of the servo readersin each of the groups and the prespecified width are both measured in adirection perpendicular to the direction of travel of the magnetic tape.

In another general embodiment, a product includes: a magnetic tapehaving a plurality of servo bands, each of the servo bands including ahigh density servo pattern and at least one timing based servo pattern.A combined width of the high density servo pattern and the at least onetiming based servo pattern in a given servo band is less than or equalto two thirds of a prespecified width of each of the servo bands.Moreover, the combined width and the prespecified width are eachmeasured in a direction perpendicular to a longitudinal axis of themagnetic tape.

In yet another general embodiment, a product includes: a magnetic tapehaving a plurality of servo bands, each of the servo bands includes ahigh density servo pattern and two timing based servo patterns. Alongitudinal axis of each of the two timing based servo patterns isparallel to a longitudinal axis of the high density servo pattern.Moreover, the two timing based servo patterns are positioned on oppositesides of the high density servo pattern along the directionperpendicular to the longitudinal axis of the magnetic tape. A combinedwidth of the high density servo pattern and one of the two timing basedservo patterns in a given servo band is less than or equal to two thirdsof a prespecified width of each of the servo bands, the combined widthand the prespecified width each being measured in a directionperpendicular to a longitudinal axis of the magnetic tape.

Referring now to FIG. 1, a schematic of a network storage system 10 isshown according to one embodiment. This network storage system 10 isonly one example of a suitable storage system and is not intended tosuggest any limitation as to the scope of use or functionality ofembodiments of the invention described herein. Regardless, networkstorage system 10 is capable of being implemented and/or performing anyof the functionality set forth herein.

In the network storage system 10, there is a computer system/server 12,which is operational with numerous other general purpose or specialpurpose computing system environments or configurations. Examples ofwell-known computing systems, environments, and/or configurations thatmay be suitable for use with computer system/server 12 include, but arenot limited to, personal computer systems, server computer systems, thinclients, thick clients, handheld or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server 12 may be described in the general context ofcomputer system-executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 12 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 1, computer system/server 12 in the network storagesystem 10 is shown in the form of a general-purpose computing device.The components of computer system/server 12 may include, but are notlimited to, one or more processors or processing units 16, a systemmemory 28, and a bus 18 that couples various system components includingsystem memory 28 which is coupled to processor 16.

Bus 18 represents one or more of any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, anaccelerated graphics port, a processor or local bus using any of avariety of bus architectures, etc. By way of example, which is in no wayintended to limit the invention, such architectures include IndustryStandard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus,Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA)local bus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 12 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 12, and may include both volatileand non-volatile media, removable and non-removable media.

System memory 28 may include computer system readable media in the formof volatile memory, such as random access memory (RAM) 30 and/or cachememory 32. Computer system/server 12 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 34 may be provided forreading from and writing to a non-removable, non-volatile magneticmedia—not shown and typically called a “hard disk,” which may beoperated in a hard disk drive (HDD). Although not shown, a magnetic diskdrive for reading from and writing to a removable, non-volatile magneticdisk (e.g., a “floppy disk”), and an optical disc drive for reading fromor writing to a removable, non-volatile optical disc such as a compactdisc read-only memory (CD-ROM), digital versatile disc-read only memory(DVD-ROM) or other optical media may be provided. In such instances,each disk drive may be connected to bus 18 by one or more data mediainterfaces. As will be further depicted and described below, memory 28may include at least one program product having a set (e.g., at leastone) of program modules that are configured to carry out the functionsof embodiments described herein.

Program/utility 40, having a set (at least one) of program modules 42,may be stored in memory 28 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, program data, etc. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. It should also be noted that program modules 42 may be usedto perform the functions and/or methodologies of embodiments of theinvention as described herein.

Computer system/server 12 may also communicate with one or more externaldevices 14 such as a keyboard, a pointing device, a display 24, etc.;one or more devices that enable a user to interact with computersystem/server 12; and/or any devices (e.g., network card, modem, etc.)that enable computer system/server 12 to communicate with one or moreother computing devices. Such communication may occur via Input/Output(I/O) interfaces 22. Still yet, computer system/server 12 maycommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 20. As depicted, network adapter 20communicates with the other components of computer system/server 12 viabus 18. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 12. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,redundant array of independent disks (RAID) systems, tape drives, dataarchival storage systems, etc.

Looking to FIG. 2, a tape supply cartridge 120 and a take-up reel 121are provided to support a magnetic tape 122. One or more of the reelsmay form part of a removable cartridge and are not necessarily part ofthe tape drive 100. A tape drive, e.g., such as that illustrated in FIG.2, may further include drive motor(s) to drive the tape supply cartridge120 and the take-up reel 121 to move the magnetic tape 122 over a tapehead 126 of any type. Such head may include an array of readers,writers, or both.

Guides 125 guide the magnetic tape 122 across the tape head 126. Suchtape head 126 is in turn coupled to a controller 128 via a cable 130.The controller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 may control head functions such as servo following, data writing,data reading, etc. The controller 128 may include at least one servochannel and at least one data channel, each of which include data flowprocessing logic configured to process and/or store information to bewritten to and/or read from the magnetic tape 122. The controller 128may operate under logic known in the art, as well as any logic disclosedherein, and thus may be considered as a processor for any of thedescriptions of tape drives included herein according to variousembodiments. The controller 128 may be coupled to a memory 136 of anyknown type, which may store instructions executable by the controller128. Moreover, the controller 128 may be configured and/or programmableto perform or control some or all of the methodology presented herein.Thus, the controller 128 may be considered to be configured to performvarious operations by way of logic programmed into one or more chips,modules, and/or blocks; software, firmware, and/or other instructionsbeing available to one or more processors; etc., and combinationsthereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the magnetic tape 122 and to receive dataread by the head 126 from the magnetic tape 122. An actuator 132controls position of the head 126 relative to the magnetic tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (internal or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

Referring momentarily to FIG. 3, an illustrative tape layout is depictedin accordance with one embodiment. As shown, magnetic tape 300 has atape layout which implements five servo bands Servo Band 0-Servo Band 4,and four data bands Data Band 0-Data Band 3, as specified in the LTOformat and IBM Enterprise format. The height H of each of the servobands is measured in the cross-track direction 304 which is aboutorthogonal to the length L of the magnetic tape 300. According to anexample, the height H of each of the servo bands may be about 186microns according to the LTO format of generations 1 to 5. Moreover, apitch β between the servo bands as shown may be about 2859 microns,again according to the LTO format of generations 1 to 5.

An exemplary tape head 302 is also shown as having two modules and asbeing positioned over a portion of the magnetic tape 300 according toone approach. Read and/or write transducers may be positioned on eithermodule of the tape head 302 according to any of the approaches describedherein, and may be used to read data from and/or write data to the databands. Furthermore, tape head 302 may include servo readers which may beused to read the servo patterns in the servo bands according to any ofthe approaches described herein. It should also be noted that thedimensions of the various components included in FIG. 3 are presented byway of example only and are in no way intended to be limiting.

Some tape drives may be configured to operate at low tape velocitiesand/or with nanometer head position settings. These tape drives may useservo formats that target magnetic tape media, 4 or 8 data bands, 32 or64 data channel operation, allow very low velocity operation, supportlarge-bandwidth actuator operation, and improve parameter estimation tominimize standard deviation of the position error signal (PES), thusenabling track-density scaling for tape cartridge capacities up to 100TB and beyond.

However, according to some embodiments, magnetic tape may further beaugmented with additional features that provide additionalfunctionality. Accordingly, HD servo patterns may be implemented inplace of the standard TBS servo patterns, e.g., as seen in FIG. 3. TheHD servo patterns may be used to improve track-following performance.

In still further embodiments, a standard TBS servo pattern (e.g., asshown in FIG. 3) may be implemented in combination with one or more HDservo patterns (e.g., see FIG. 4A below). One implementation includes ahybrid servo pattern scheme, in which a standard TBS pattern is retainedand additional HD patterns are provided in a dedicated, preferablycurrently unused area of the magnetic tape media. This type of patternmay be implemented by increasing the number of data channels from 16 to32, and reducing the width of the TBS pattern from 186 microns to 93microns, in some approaches.

A hybrid servo pattern 410, which includes a standard TBS pattern 402written in a servo band, as well as an HD pattern 404 that is written ina HD band (e.g., dedicated area) of the magnetic tape medium 408 isshown in FIG. 4A. Moreover, each HD pattern 404 includes a number of HDtracks, each of the HD tracks having a respective periodic waveform,e.g., as seen in FIGS. 5A, 5C and 11A below. In some approaches,significant features of the original TBS pattern 402 are retained, suchas a servo frame structure consisting of four servo bursts containing anumber of servo stripes, where the servo stripes of adjacent servobursts are written with alternating azimuthal angle. Other parameters oflegacy servo patterns, such as the servo pattern height and othergeometric dimensions, as well as the number of servo stripes per burst,may be modified as desired.

The HD pattern 404 may include periodic waveforms of various frequenciesalternately written in the length direction L along a longitudinal axisof the magnetic tape. The standard TBS pattern 402 may be used toprovide initial identification of the servo band (e.g., by providing aservo band ID); initial positioning of the head 406 on an appropriateservo location; acquisition of initial servo channel parameters, such astape velocity, lateral head position, head-to-tape skew, longitudinalposition (LPOS), etc.; etc. Moreover, the HD pattern 404 may enable moreaccurate and more frequent estimates of servo channel parameters,thereby achieving improved head positioning at a much wider range oftape velocities and support for larger bandwidth head actuation. Assuch, track-density scaling may be enabled for very large cartridgecapacities, as well as improved data rate scaling with host computerrequirements through the support of a wider velocity range.

The detection of the periodic waveforms forming a HD pattern may beobtained by a detector that implements a complex algorithmic conversion,e.g., such as a Discrete Fourier Transform (DFT), a Fast FourierTransform (FFT), etc. However, this implementation complexity may reducethe flexibility in trade-offs between the rate of generation of servoreader lateral position estimates and the standard deviation of theestimation error. Accordingly, components (e.g., controllers) with highthroughput may desirably be used to process signals derived from a HDpattern in order to reduce the processing time thereof.

In one embodiment, a detector capable of reading a hybrid of TBS and HDpatterns may be implemented. The hybrid detector may be configured toobtain estimates of the energy of relevant spectral frequency componentsin a readback signal from the HD pattern, while also calculatingestimates of the lateral position of the head based on these energies,without applying a DFT or a FFT.

Samples provided at the input of the components performing the spectralestimation may be obtained at the proper sampling instants byinterpolating the sequence of readback HD servo signal samples from ananalog-to-digital (A/D) converter at a fixed clock frequency in oneembodiment, or at a variable clock frequency in another embodiment. Thetime base of the interpolator may be derived from the estimate of thetape velocity provided by the TBS channel operating in parallel with theHD detector, in some embodiments, as will be described in further detailbelow.

Various trade-offs between the rate of generation of spectral estimates,from which servo reader lateral position estimates are obtained, and thestandard deviation of the estimation error are possible. However, asuitable and preferred implementation may be achieved with asignificantly reduced complexity compared to DFT-based or FFT-basedimplementations. Specifically, in one embodiment, only a small set ofspectral estimates are computed, compared to the fixed set ofequally-spaced spectral components computed by a DFT or FFT.Furthermore, the integration interval may be freely adjusted, while aDFT/FFT-based solution involves the integration interval being multiplesof the DFT/FFT size.

Even when the HD servo pattern uses a large number of tone frequencies,the maximum number of spectral estimates that are computed by theproposed detector may correspond to the maximum number of tracks that anHD servo reader reads simultaneously at any time. Also, the proposeddetector may be reconfigured to provide spectral estimates correspondingto the tracks currently being read based on the coarse positioninginformation from the TBS channel.

Referring again to FIG. 4A, which shows a tape layout 400 with a hybridservo pattern 410 according to one embodiment, in the hybrid servopattern 410, an HD pattern 404 is written in a space adjacent to astandard TBS pattern 402. According to the present embodiment,quadrature sequences are not included due to the use of the TBS pattern402, which is converse to products implementing servo functionality inhard-disk drives.

Looking momentarily to FIG. 4B, a partial detailed view of a TBS pattern402 (e.g., a TBS frame) is illustrated according to an exemplaryembodiment. As shown, a plurality of servo stripes 412 together form aservo burst 414, while corresponding pairs of servo bursts 414 formservo sub-frames. In the present embodiment, the servo bursts 414included in the left servo sub-frame each have five servo stripes 412,while the servo bursts 414 included in the right servo sub-frame eachhave four servo stripes 412. However, in some approaches each servosub-frame may include the same number of servo stripes 412. The servostripes 412 included in a given servo burst 414 are oriented such thatthey have a same azimuthal slope represented by angle α. A distance d/2separating the leftmost servo stripes 412 of adjacent servo bursts 414varies depending on the approach. Moreover, corresponding pairs of servobursts 414 have opposing azimuthal slopes, thereby forming achevron-type pattern. The height H and thickness t of the servo stripes412 may vary depending on the servo writer used to write the TBS pattern402. The spacing S between each of the servo stripes 412 and/or thesub-frame length SFL between servo bursts 414 having the same azimuthalslope may also vary depending on the desired approach.

Table 1 below provides several exemplary values for various ones of thedimensions identified in FIG. 4B according to two different approaches.Each of the approaches corresponds to a magnetic tape having a differentnumber of data channels, e.g., as would be appreciated by one skilled inthe art. Moreover, it should be noted that the various dimensionalvalues in Table 1 below are provided by way of example only and are inno way intended to limit the invention. Thus, according to various otherapproaches, any desired dimensional value may be implemented.

TABLE 1 Number of α H d/2 SFL S data channels (degrees) (μm) (μm) (μm)(μm) 64 18 46.5 29.5 59.0 2.4 128 24 25.0 25.5 51.0 2.4

According to an exemplary approach, which is in no way intended to limitthe invention, the height H may be about 186 μm, and the angle α may beabout 6°, while the thickness t is about 2.1 μm. According to anexemplary approach, which is in no way intended to limit the invention,the spacing S may be about 5 μm, while the sub-frame length SFL is about100 μm. As described above, patterned transitions such as that shown inFIG. 4B allow for an estimate of the head lateral position to bedetermined by evaluating the relative timing of pulses generated by aservo reader reading the servo stripes 412 of the servo burst 414 asthey are passed over the servo reader.

Referring again to FIG. 4A, the HD pattern 404 may include periodicwaveforms written on adjacent tracks. For example, two periodicwaveforms, characterized by two different spatial frequencies:low-frequency f₁ and high-frequency f₂, where f₂>f₁. However, a widerrange of lateral head displacement is desired. Accordingly, a differentconfiguration of the HD patterns may be used to avoid ambiguity indetermining the lateral displacement.

An HD servo pattern preferably includes periodic waveforms of differingfrequencies alternately written in the lateral (cross-track) direction.Accordingly, HD servo patterns may be able to desirably provide moreaccurate and/or more frequent estimates of servo channel parametersaccording to various embodiments described herein. Looking to FIGS.5A-5D, an HD pattern 500 is shown that overcomes the limited range oflateral head displacement associated with an HD pattern having only twoperiodic waveforms, characterized by two different spatial frequencies.As shown in FIGS. 5A and 5C, at least three frequencies are used for theHD pattern 500 in adjacent tracks, which repeat periodically across theband where the HD pattern is written. In the embodiment of FIGS. 5A and5C, the servo reader (denoted by the block labelled ‘R’) spans wider inthe cross-track direction 502 than a single track, such that at leasttwo tones are detected under any reading conditions at a given time whenthe servo reader R is overlapped with the HD pattern 500. Lookingspecifically to FIG. 5A, the reader R spans across both the bottomportion 508 and middle portion 506 of the HD pattern 500. FIG. 5Cillustrates an alternative position for the servo reader R, where thereader R spans across the upper portion 504 and middle portion 506 ofthe HD pattern 500.

The three portions 508, 506, 504 of the periodic waveforms arecharacterized by three different frequencies f₁, f₂, and f₃,respectively, where f₃>f₂>f₁. According to various approaches, eachwaveform may be characterized as having a number of periods in a rangefrom about 25 to about 200, such as 30 periods, 50 periods, 75 periods,100 periods, etc., within a predetermined spacing. More preferably, thepredetermined spacing may be in a range from about 50 μm to about 150μm, such as about 60 μm, about 75 μm, about 100 μm, etc., depending onthe approach. Moreover, the symbol length may be in a range from about0.5 μm to about 3.0 μm, e.g., such as about 1.0 μm, about 1.5 μm, about2.0 μm, etc.

Hence, with continued reference to FIGS. 5A-5D, an edge of one of theportions of the HD pattern 500 may be distinguished from the edge ofanother of the portions. Looking specifically to FIG. 5A, an edge of themiddle portion 506 may be distinguished from an edge of the bottomportion 508 by evaluating the signals read by the servo reader R, whichoverlaps both portions 506, 508. The graph 510 in FIG. 5B identifies thevarious frequencies in the readback signal from servo reader R and theenergy level corresponding to each of the respective frequencies for theposition of the servo reader R shown in FIG. 5A. Energy values may bedetermined in some approaches by integrating over a given amount of time(or distance along the magnetic tape). As shown in graph 510, inaddition to the middle frequency f₂, the bottom frequency f₁ is presentin the readback signal of the servo reader R and may thereby be detectedby a spectral analysis. Furthermore, the energy values of the spectralcomponents f₁ and f₂ represent the relation of the servo reader Roverlapping the middle and bottom portions 506, 508. Given that theenergy value of the spectral component of frequency f₁ is smaller thanthe energy value of the spectral component of the second frequency f₂,it follows that the servo reader R can be determined to be overlappedwith the middle portion 506 more than it is overlapped with the bottomportion 508. Moreover, a comparison of the corresponding energies may beused to determine a fine position of the servo reader R with respect toa magnetic tape.

Similarly, the graph 520 in FIG. 5D identifies the frequencies in thereadback signal from servo reader R positioned as shown in FIG. 5C, aswell as the energy level corresponding to each of the respectivefrequencies. As shown, frequencies f₂, and f₃ are present in thereadback signal of the servo reader R, and may be detected by a spectralanalysis. Again, the energies of the spectral components for frequenciesf₂, and f₃ indicate that the servo reader R is positioned above theupper and middle portions 504, 506. Given that the energy of thespectral component of frequency f₃ is smaller than the energy of thespectral component of frequency f₂, it follows that the servo reader Ris overlapped with the middle portion 506 more than it is overlappedwith the upper portion 504. Moreover, a comparison of the correspondingenergy values may be used to determine a fine position of the servoreader R with respect to a magnetic tape.

Note that the waveform periods of the three frequencies may be integermultiples of a period T, for example T=241.3 nm, which corresponds tothe highest spatial frequency, which is proportional to 1/T, whenspectral estimation by a DFT/FFT-based detector with a minimum number ofspectral bins for given integration interval is adopted.

FIG. 6 shows a block diagram of a DFT/FFT-based detector 600 configuredfor the computation of the PES from an HD servo pattern comprisingperiodic waveforms. The servo signal from the servo reader 602 isinterpolated using a servo signal interpolator 604 with the timinginformation from a synchronous servo channel 606. The interpolatedsignal samples are then processed by either a DFT-based or a FFT-based(DFT/FFT-based) detector 608 that estimates the signal energy values atfrequencies f₁ and f₂. The DFT/FFT-based detector 608 outputs are inputto a PES computation unit 610, which determines a PES estimate by takingthe difference of the signal energy values.

Ideally, the two periodic waveforms, whose energies are estimated by theDFT/FFT-based detector 608, are sinusoidal waveforms at frequencies f₁and f₂. However, a DFT/FFT-based detector 608 when used for HD patternshas an inherent drawback where the number of spectral components, forwhich an estimate of the energy is provided, depends on the integrationinterval for the DFT (or FFT) computation, and may be very large whenthe integration interval extends over several periods of the fundamentalfrequency, as is typically the case when a low-noise estimation processis used.

As the number of periodic waveform components forming the readbacksignal of an HD pattern is usually limited to two or three for a givenlateral position, it is advantageous to resort to a low-complexityimplementation of the detector, whereby only estimates of the energy ofthe relevant spectral components at two or three frequencies in thereadback signal of an HD pattern are efficiently computed.

Now referring to FIG. 7, a detector 700 for HD patterns is shownaccording to one embodiment. The detector 700 is configured to operatewith periodic waveforms, which correspond to the components of thereadback signal of an HD pattern, that are characterized by threefrequencies at any time, as illustrated for example in FIGS. 5A-5Baccording to one embodiment. With continued reference to FIG. 7, thedetector 700 includes three digital filters 702, 704, 706 with lowimplementation complexity, each digital filter comprising a second-orderinfinite impulse response (IIR) stage followed by a two-tap finiteimpulse response (FIR) stage, for the estimation of the energy of thereadback HD servo signal at a specific frequency according to theGoertzel algorithm. Other arrangements and components may be used forthe three digital filters 702, 704, 706 as would be understood by one ofskill in the art upon reading the present descriptions. The waveformperiods (in nm) corresponding to the three frequencies may be assumed tobe integer multiples of a fundamental period, T.

For an accurate estimation of the energies of the three periodicwaveform components in a finite integration interval, the frequencies ofthe periodic waveform components preferably match the characteristicfrequencies of the three digital filters 702, 704, 706, denoted byω₀/2n, ω₁/2π, and ω₂/2π, respectively. When a match is not possible, itis preferred that the frequencies are within about 0.001% to 1.0% of thefrequencies set for the three digital filters 702, 704, 706, and morepreferably a difference of less than about 0.1%. This may be achieved byresampling the output sequence of the analog-to-digital converter (ADC)708 at appropriate time instants, which may be provided by aninterpolator 710, with a time base obtained from the tape velocity and agiven interpolation distance Δx_(HD), as shown in FIG. 7. The frequencyf_(s) of the clock 718, is used as an input to the ADC 708, the counter720, and the digital circuitry of the detector 700. Moreover thefrequency f_(s) of the clock 718 may be either a fixed frequency or avariable frequency.

In one embodiment, the interpolator 710 may be a cubic Lagrangeinterpolator to achieve smaller signal distortion than a linearinterpolator. Of course, any suitable interpolator may be used, as wouldbe understood by one of skill in the art. The output signal samples ofthe interpolator 710 are obtained that correspond with HD servo signalsamples taken at points on the magnetic tape that are separated by astep interpolation distance equal to Δx_(HD), independently of the tapevelocity. Δx_(HD) is preferably selected such that the conditionT/Δx_(HD)=K is satisfied independently of the tape velocity, where K isa positive integer number. The time base for the generation of theinterpolator output samples may be provided by an interpolation timecomputation unit 712, which yields the sequence of time instants{t_(n)}, at which the resampling of the ADC output sequence takes place.Time instants {t_(n)} may furthermore be provided to circular buffer722.

The detector 700 illustrated in FIG. 7 may be configured such that agiven number of samples is computed by the interpolator 710 within aclock interval T_(s)=1/f_(s). However, doing so may set a limit on themaximum tape velocity at which the detector 700 may operate, the maximumtape velocity represented by 2Δx_(HD)/T_(s). The maximum tape velocitysupported by the detector 700 may be increased by allowing a largernumber of samples to be computed by the interpolator 710 within a singleclock interval, but doing so also increases computational complexity.

For a fixed tape velocity, the time instants {t_(n)} may be uniformlyspaced by T_(I) seconds, where T_(I) denotes the time interval that ittakes for the magnetic tape to travel over a distance equal to the stepinterpolation distance Δx_(HD). The estimation of the time intervalT_(I) is performed by a step interpolation time computation unit 714,which computes T_(I)=Δx_(HD)/ν_(est), i.e., the ratio between Δx_(HD)and the estimate of the instantaneous tape velocity ν_(est), which maybe obtained from the TBS channel in one approach. The TBS channel mayoperate as a synchronous TBS channel according to one embodiment. Theaverage number of interpolated signal samples generated per ADC clockinterval is given by the ratio T_(I)/T_(s), where T_(s)=1/f_(s) denotesthe clock interval. The ADC clock frequency, f_(s), may be a fixedfrequency in one approach, or a variable frequency in another approach.

In one embodiment, the HD detector 700 may be configured to estimate thetape velocity to determine time instants at which to obtain interpolatedsignal samples to input to the Goertzel algorithm, as filtering elementsbased on an output of a TBS channel of the tape drive configured toprocess a TBS pattern written on the servo band of the magnetic tapemedium may not be available.

In another embodiment, the HD detector 700 may be configured to computea head lateral position estimate for coarse positioning of the servoreader based on an output of a TBS channel of the tape drive. Also, theHD detector 700 may be configured to adjust settings for at least onedigital filter according to waveform frequency components of the HDservo signal estimated based on the head lateral position estimate. Forexample, the setting ω_(i) of the i-th digital filter may be adjustedbased on the coarse position estimate and the known frequencyω_(i)=2πf_(i) of the HD patterns located at that estimated (coarse)lateral position. In another example, the settings of the i-th digitalfilter may be adjusted based on the coarse position estimate and thecombination of symbol length, integration interval, etc., of the HDpatterns located at that estimated (coarse) lateral position.

The HD detector 700 receives, as inputs, values of the threecharacteristic frequencies {ω₀, ω₁, ω₂}, with ω_(i)=2πf_(i) from whichthe coefficients of the digital filters 702, 704, 706 are obtained.These frequencies may be obtained from the knowledge of the servo readerlateral position provided by the TBS channel in one embodiment, asdescribed above. Assuming the number “Q” represents the number ofsamples over which the estimates of the energies of the periodicwaveforms are computed, Q may determine the length of the integrationinterval, and therefore may also determine the spatial frequencyresolution. Assuming the value of Q is even, Q/2 represents the numberof frequencies for which energy estimates would be provided by aDFT/FFT-based HD detector that operates over Q samples. Q may beobtained from the tape drive memory in one embodiment. Moreover, Q istypically about 100 or larger.

Multiplication of the three energy estimates by gain factors g_(i), fori=0, 1, 2, is provided to compensate for the different attenuations thatthe readback HD servo signal may experience at different frequencies,where the normalization g₁=1 may be assumed. Hence, a lateral positionestimate of the HD servo reader 716, and hence a position error signalfrom the knowledge of the target head position, may be obtained by alinear combination of the three energy estimates. Note that the maximumnumber of spectral estimates that are computed at any time is determinedby the maximum number of tracks that may be read by the HD servo reader716, which may equal three in some approaches, and not by the overallnumber of tones in the HD servo pattern, which may be larger than three.In a case where the number of tones is larger than three, the values ofthe three characteristic frequencies {ω₀, ω₁, ω₂} that are provided tothe HD detector 700 may be derived from knowledge of the lateralposition estimate obtained from the TBS channel, as mentioned above.

In another embodiment, the HD detector 700 may be implemented without aninterpolator 710, but with digital filters configurable to adjust theirsettings according to the waveform spatial frequency components of theHD servo signal read from the magnetic tape medium and the tapevelocity. Adjustment of the digital filters settings may be based on acoarse head lateral position estimate and/or a tape velocity estimatecomputed based on an output of a TBS channel of the tape drive.

In an alternate embodiment, an HD detector may implement additionaldigital filters, in excess to the digital filters used to estimate theenergies at the frequencies corresponding to the patterns written on thetracks being read simultaneously by the HD servo reader 716. The one ormore excess digital filters may be used to simplify reconfiguration ofthe detector when the target lateral position changes and, therefore,the input values of frequencies {ω_(x)} vary dynamically.

In a further embodiment, the one or more excess digital filters may beused to distinguish HD patterns characterized by a small number ofspectral components/lines from broadband noise and/or data signals. Thismay be achieved by choosing the characteristic frequency ω_(i) of theexcess digital filter such that it measures a spectral component at afrequency that is not used by the HD patterns.

The outputs |X_(i,t)|² from the three digital filters 702, 704, 706 areprovided to a PES computation unit 724, which provides a position errorestimate (ε_(t)) at given time t.

Other components of the HD detector 700 may operate as would be known toone of skill in the art, and are omitted here for the sake of clarity ofthe described embodiments.

As described above, in the past tape skew and TDS measurements have beendetermined from the information from servo bands on both sides of a headmodule, or information from servo readers on multiple head modules. Inother words, to compute skew and/or TDS, conventional products haveneeded to obtain valid servo information from more than one servo bandand/or more than one head module. This makes such conventional headmodules particularly susceptible to degraded performance and/or beingrendered completely useless by servo defects, scratches caused byasperities on the surface of the magnetic tape, etc.

Although hybrid servo patterns provide some additional information whichmay be used to improve track following performance, conventionalproducts have been unable to implement such hybrid servo patterns whilealso achieving backward compatibility. Backward compatibility is highlydesirable for removable storage media such as magnetic tape. Forinstance, backward compatibility allows a given tape drive to supportmultiple different generations of magnetic tape. Accordingly, backwardcompatibility allows users to maximize flexibility of tape mediaresource arrangements available to them.

To achieve backward compatibility among multiple generations of magnetictape, it is desirable that a number of data bands relative to servobands maintains a standard ratio while also complying with datatransducer configurations employed to achieve further increases in datacapacity of the magnetic tapes. Moreover, it is desirable that servoreaders on a single head module are compatible with various differentservo band formats. However, this has served as a significant issue forconventional products thus far. Accordingly, achieving a magnetic tapeproduct and/or system which is able to continue to increase datacapacity, while also improving data track following performance, as wellas maintaining a standard ratio of data bands relative to servo bands isgreatly desired.

Looking momentarily to FIG. 8A, a partial representational view of aconventional servo band 800 is illustrated. The conventional servo band800 includes a TBS pattern 802 having a width W_(C) which extends in thecross-track direction 804. The width W_(C) of the conventional TBSpattern 802 is about two thirds of a width W of the servo band 800itself as shown in FIG. 8A. Therefore, a portion (about one third) ofthe servo band 800 remains unused. Moreover, FIG. 8B illustrates aportion of a conventional head module 850 positioned over theconventional servo band 800. As shown, the module 850 includes a singleservo reader 852 which is positioned over the conventional TBS pattern802. The module 850 also includes 32 data transducers 854 (not all ofwhich are shown) extending along the cross-track direction 804.

As previously mentioned, conventional products implementing conventionalservo bands and conventional head modules, e.g., such as thoseillustrated in FIGS. 8A-8B, determine tape skew and TDS measurementsfrom the information read from servo bands on both sides of a headmodule, or information read from servo readers on multiple head modules.In other words, to compute skew and/or TDS, conventional products haveneeded to obtain valid servo information from more than one servo bandand/or more than one head module. This makes such conventional headmodules particularly susceptible to degraded performance and/or beingrendered completely useless by servo defects, scratches caused byasperities on the surface of the magnetic tape, etc. For example, shouldthe single servo reader 852 of FIG. 8B no longer be able to read theconventional TBS pattern 802, the conventional head module 850 iseffectively rendered useless.

It should be noted that the embodiments illustrated in FIGS. 8A-8B arepresented simply to illustrate a conventional product by way of example,and are no way intended to limit the invention. In sharp contrast to theforegoing conventional products illustrated in FIGS. 8A-8B, variousembodiments described and/or suggested herein achieve significantimprovements to track following performance, increased data capacity,backward compatibility, etc., as will be described in further detailbelow.

Looking now to FIG. 9A, a product 900 is illustrated in accordance withone embodiment. As an option, the present product 900 may be implementedin conjunction with features from any other embodiment listed herein,such as those described with reference to the other FIGS., such as FIGS.1-7. However, such product 900 and others presented herein may be usedin various applications and/or in permutations which may or may not bespecifically described in the illustrative embodiments listed herein.Further, the product 900 presented herein may be used in any desiredenvironment. Thus FIG. 9A (and the other FIGS.) may be deemed to includeany possible permutation.

As shown, product 900 of FIG. 9A includes a magnetic tape 902 having aplurality of servo bands 904 and data bands 906 which run (extend)parallel to each other along the longitudinal axis 908 of the magnetictape 902. According to the present approach, the magnetic tape 902includes 5 servo bands 904 and 4 data bands 906, but may include anydesired number of servo bands and/or data bands depending on the desiredapproach.

When produced, the extents of the servo bands 904 and/or data bands 906(represented in FIG. 9A by the dashed lines running parallel to thelongitudinal axis 908 of the magnetic tape 902) may not be defined byanything that is actually formed (e.g., written) along the length of themagnetic tape 902 itself. Rather, the extents of the servo bands 904and/or data bands 906 may be defined by a format which the magnetic tape902 corresponds to. For example, a format corresponding to FIG. 9A mayspecify that the magnetic tape 902 includes the 5 servo bands 904 and 4data bands 906 depicted. Moreover, the format may include a prespecifiedwidth W for each of the 5 servo bands 904, measured in the cross-trackdirection 910 which is perpendicular to the longitudinal axis 908 of themagnetic tape 902 (along with the direction of travel of the magnetictape 911). In some approaches, the format may also include aprespecified width (not shown) for each of the 4 data bands 906,preferably measured in the cross-track direction 910. Moreover, itshould be noted that the prespecified width W is preferably the same foreach of the 5 servo bands 904 on the magnetic tape 902. According to anexample, which is in no way intended to limit the invention, theprespecified width W may be about 93 μm. According to another example,the prespecified width W may be about 140 μm.

The prespecified width W of the servo bands 904 effectively defines theouter lateral edges of the servo band itself. Thus, data may be writtenimmediately adjacent the outer extents of the servo bands 904 along thecross-track direction 910 in some approaches. In other approaches, themagnetic tape 902 may implement guard bands which separate the servobands 904 from the data bands 906 along the cross-track direction 910.Referring momentarily to FIG. 9B, Servo Band 3 is shown as beingseparated from Data Band 0 and Data Band 2 by guard bands 912 whichextend along the length of the magnetic tape 902. Moreover, aspreviously mentioned, the prespecified width of the servo band 904preferably does not include the lateral extent of the magnetic tape 902occupied by the guard bands 912.

Referring again to FIG. 9A, the outermost servo bands 904 may similarlybe recessed from the outer lateral extents of the magnetic tape 902 by alateral offset 914 as shown. The lateral offsets 914 may prevent reducedtape-drive performance caused by the magnetic tape 902 traveling up theflanges of a tape guide (e.g., see 125 of FIG. 2). However, theprespecified width of the servo bands 904 preferably does not includethe lateral extent of the magnetic tape 902 occupied by the offsets 914either.

The format of a magnetic tape may be stored differently in differentapproaches. In some approaches, the format corresponding to the magnetictape 902 of FIG. 9A may be written in a header of the magnetic tapeitself during production of the magnetic tape 902, whereby the formatmay be read by a magnetic tape head accessing the magnetic tape 902. Inother approaches, the format corresponding to the magnetic tape 902 maybe stored in memory coupled to a cartridge which houses the magnetictape 902. For instance, referring momentarily to FIG. 15, the datastorage cartridge 1500 includes a cartridge memory 1504 shown in acutaway portion of the Figure, which is in no way intended to limit theinvention. Further still, in other approaches the format correspondingto a magnetic tape may be stored in a barcode coupled to a magnetic tapecartridge. Therefore, as alluded to above, the prespecified width of theservo bands of a given magnetic tape may be determined by accessing theformat corresponding to the magnetic tape from any of the foregoingpotential storage locations. Moreover, format information may generallybe used to look up specific formatting dimensions which correspond tothe given type (e.g., generation, style, etc.) of magnetic tape.

Although the lateral extents of the servo bands 904 and/or data bands906 may not actually be formed on the magnetic tape 902, the magnetictape 902 preferably does have servo patterns (not shown in FIG. 9A)formed in the servo bands 904 along the length of the magnetic tape 902.The servo patterns may be written by a servo writer and may havedifferent forms, thereby resulting in the servo bands having differentconfigurations depending on the approach, e.g., as will soon becomeapparent.

Looking now to FIGS. 9C-9F, several different servo band configurations920, 930, 940, 950 are illustrated in accordance with differentapproaches of the product illustrated in FIG. 9A. It should be notedthat any of the different servo band configurations 920, 930, 940, 950illustrated in FIGS. 9C-9F may be implemented in the servo bands 904 ofthe magnetic tape 902 in FIG. 9A. Further, the servo band configurations920, 930, 940, 950 illustrated in FIGS. 9C-9F may be used in any desiredenvironment.

Each of the servo band configurations 920, 930, 940, 950 depicted inFIGS. 9C-9F include a HD servo pattern and at least one TBS servopattern. Two of the servo band configurations 920, 940 include a secondTBS pattern, which is in no way intended to limit the invention.Moreover, a combined width of the HD servo pattern and one of the atleast one TBS servo pattern in a given servo band is preferably lessthan or equal to two thirds of a prespecified width of the given servoband, as will be described in further detail below.

Referring specifically to FIG. 9C, the servo band configuration 920 isof a second type and includes a HD servo pattern 922 along with a firstTBS servo pattern 924 and a second TBS servo pattern 926. As shown, theHD servo pattern 922 is sandwiched between the first and second TBSservo patterns 924, 926 along the cross-track direction 910, such thatthe two TBS patterns 924, 926 are positioned on opposite sides of the HDservo pattern 922 in the cross-track direction 910. Moreover, alongitudinal axis of each of the two TBS patterns 924, 926 is parallelto a longitudinal axis of the HD servo pattern 922.

A width W_(HD2) of the HD servo pattern 922 (measured in the cross-trackdirection 910) may be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Moreover, awidth W_(TBS2) of the first TBS servo pattern 924 and a width W_(TBS2′)of the second TBS servo pattern 926 (both measured in the cross-trackdirection 910) are each less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Accordingly,a combined width of the HD servo pattern 922 and one of the TBS servopatterns 924, 926 may be less than or equal to two thirds of theprespecified width W of the servo band. The upper TBS pattern 926 may belocated in a region of the servo band that otherwise is reserved as anunused region. Therefore, the servo band configuration 920 may extendfully across the prespecified width W of the servo band. For approachesin which the magnetic tape does not include a guard band, one or both ofthe TBS patterns 924, 926 may abut (e.g., be immediately adjacent) alocation where a first data track may be written in the adjacent databand. However, for approaches in which a data band is present, one orboth of the TBS patterns 924, 926 may still be separated from thelocation where a first data track may be written by a guard band, e.g.,as would be appreciated by one skilled in the art after reading thepresent description.

Now looking to FIG. 9D, the servo band configuration 930 is of a thirdtype and includes a HD servo pattern 932 along with a TBS servo pattern934. As shown, the HD servo pattern 932 is positioned immediatelyadjacent a side of the TBS servo pattern 934 on which the ends of theservo bursts 936 are closest together. However, in other approaches theHD servo pattern 932 may be positioned on the opposite side of the TBSservo pattern 934 (on which the ends of the servo bursts 936 arefarthest apart). Moreover, a longitudinal axis of the TBS pattern 934 isparallel to a longitudinal axis of the HD servo pattern 932.

A width W_(HD3) of the HD servo pattern 932 (measured in the cross-trackdirection 910) may be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Moreover, awidth W_(TBS3) of the TBS servo pattern 934 is also less than or equalto one third of the prespecified width W of the given servo band ServoBand 4. Accordingly, a combined width of the HD servo pattern 932 andthe TBS servo pattern 934 may be less than or equal to two thirds of theprespecified width W of the servo band.

Referring specifically to FIG. 9E, the servo band configuration 940 isof a fourth type and includes a HD servo pattern 942 along with a firstTBS servo pattern 944 and a second TBS servo pattern 946. As shown, theHD servo pattern 942 is sandwiched between the first and second TBSservo patterns 944, 946 along the cross-track direction 910, such thatthe two TBS patterns 944, 946 are positioned on opposite sides of the HDservo pattern 942 in the cross-track direction 910. Moreover, alongitudinal axis of each of the two TBS patterns 944, 946 is parallelto a longitudinal axis of the HD servo pattern 942.

A width W_(HD3) of the HD servo pattern 932 (measured in the cross-trackdirection 910) may be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Moreover, awidth W_(TBS3) of the TBS servo pattern 934 may also be less than orequal to one third of the prespecified width W of the given servo bandServo Band 4. Preferably, the width W_(HD3) of the HD servo pattern 932and the width W_(TBS3) of the TBS servo pattern 934 are each less thanor equal to one sixth of the prespecified width W of the given servoband Servo Band 4. Accordingly, a combined width of the HD servo pattern932 and the TBS servo pattern 934 may be less than or equal to twothirds, preferably the width of the servo patterns 932 and 934 are eachless than or equal to one third, of the prespecified width W of theservo band.

A width W_(HD4) of the HD servo pattern 942 (measured in the cross-trackdirection 910) may be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Moreover, awidth W_(TBS4) of the first TBS servo pattern 944 and a width W_(TBS4′)of the second TBS servo pattern 946 (both measured in the cross-trackdirection 910) may each be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. However, itis preferred that the width W_(HD4) of the HD servo pattern 942 and thewidth W_(TBS4), W_(TBS4′) of each respective one of the TBS servopatterns 944, 946 are each less than or equal to one sixth of theprespecified width W of the given servo band Servo Band 4. Accordingly,a combined width of the HD servo pattern 942 and one of the TBS servopatterns 944, 946 may be less than or equal to two thirds, preferablyless than or equal to one third, of the prespecified width W of theservo band.

Now looking to FIG. 9F, the servo band configuration 950 is of a fifthtype and includes a HD servo pattern 952 along with a TBS servo pattern954. As shown, the HD servo pattern 952 is positioned immediatelyadjacent a side of the TBS servo pattern 954 on which the ends of theservo bursts 956 are closest together. However, in other approaches theHD servo pattern 952 may be positioned on the opposite side of the TBSservo pattern 954 (on which the ends of the servo bursts 956 arefarthest apart). Moreover, a longitudinal axis of the two TBS pattern954 is parallel to a longitudinal axis of the HD servo pattern 952.

A width W_(HD5) of the HD servo pattern 952 (measured in the cross-trackdirection 910) may be less than or equal to one third of theprespecified width W of the given servo band Servo Band 4. Moreover, awidth W_(TBS5) of the TBS servo pattern 954 is also less than or equalto one third of the prespecified width W of the given servo band ServoBand 4. Preferably, the width W_(HD5) of the HD servo pattern 952 andthe width W_(TBS5) of the TBS servo pattern 954 are each less than orequal to one sixth of the prespecified width W of the given servo bandServo Band 4. Accordingly, a combined width of the HD servo pattern 952and the TBS servo pattern 954 may be less than or equal to two thirds,preferably less than or equal to one third, of the prespecified width Wof the servo band.

It should be noted that, while the various servo band configurationsillustrated in the different approaches of FIGS. 9C-9F illustrate thecorresponding servo patterns shifted to, and abutting one side of theservo band, the servo patterns may have any desired placement within theservo band. For example, in some approaches the servo bands may beshifted towards and abutting the opposite side of the servo band alongthe cross-track direction. In other approaches, the servo patterns maybe centered in the servo band along the cross-direction.

Referring back to FIG. 9A, a magnetic tape head 916 is shown as beingpositioned over the magnetic tape 902. The magnetic tape head 916 may bepart of a tape drive configured to read servo patterns written in theservo bands 904, write data to the data bands 906, read data written tothe data bands 906, etc., e.g., such as tape drive 100 of FIG. 2described above. It follows that the magnetic tape head 916 may havedata transducers (not shown) and/or servo readers oriented in differentconfigurations, e.g., depending on the servo band configuration of themagnetic tape 902, as will soon become apparent.

Looking now to FIGS. 9G-9H, two different servo reader configurations960, 970 are illustrated in accordance with different approaches of themagnetic tape head 916 illustrated in FIG. 9A. It should be noted thatany of the different servo reader configurations 960, 970 illustrated inFIGS. 9G-9H may be implemented in the magnetic tape head 916 in FIG. 9A.Further, the servo reader configurations 960, 970 illustrated in FIGS.9G-9H may be used in any desired environment.

Each of the servo reader configurations 960, 970 depicted in FIGS. 9G-9Hincludes a group of servo readers (e.g., at least two) positioned ateach opposite end of an array of data transducers. The array of datatransducers is positioned along the magnetic tape head, such that thearray of data transducers extends in the cross-track direction 910 whichis perpendicular to a direction of travel of the magnetic tape 911.Moreover, a distance between each of the immediately adjacent servoreaders in each of the groups of servo readers is preferably less thanor equal to one third of the prespecified width W of each of the servobands, as will be described in further detail below.

Referring specifically now to FIG. 9G, the servo reader configuration960 has groups 962, 964 of servo readers, each of which includes twoindividual servo readers 980, 982 and 984, 986 respectively. As shown,each of the groups of servo readers 962, 964 is positioned at anopposite end of the array 967 of data transducers 968 along thecross-track direction 910. Moreover, a longitudinal axis of each of thegroups 962, 964 of servo readers is parallel to the longitudinal axis ofthe array 967 of data transducers 968. The array 967 of data transducers968 may include data readers and/or data writers. Moreover, depending onthe desired approach, the array 967 of data transducers 968 may include32 individual data transducers, 64 individual data transducers, 128individual data transducers, etc., or any other desired number ofindividual data transducers. Moreover, one or more of the servo readersmay have a height (measured along the longitudinal axis of the magnetictape head) that is about 1.75 μm, but could be higher or lower dependingon the desired approach.

A distance D₁ (measured in the cross-track direction 910) between eachof the immediately adjacent servo readers 980, 982 and 984, 986 in eachof the groups 962, 964 respectively, may be less than or equal to onethird of a prespecified width W of the given servo band. A magnetic tapehead having immediately adjacent servo readers which are separated by adistance D₁ which is less than or equal to one third of a prespecifiedwidth W of the given servo band is highly desirable as the servo readersare thereby able to read servo patterns with added granularity andachieve improved track following efficiency for various different types(e.g., generations) of magnetic tape. For example, referring momentarilyto FIGS. 11A-11C, a magnetic tape head having two servo readers whichare separated by a distance D₁ which is less than or equal to one thirdof a prespecified width W of the given servo band is positionablerelative to a magnetic tape such that both servo readers are able toread servo information from one or more servo patterns in the givenservo band simultaneously. Accordingly, some of the servo readerscoupled to the magnetic tape head may be redundant, thereby improvingresilience against degraded performance caused by servo reader error.For example, the servo readers in a first of the groups 962, 964 may beused to read servo information from the servo patterns in acorresponding servo band, while the other one of the groups 962, 964 mayremain inactive in a backup capacity, simultaneously read servoinformation from servo patterns corresponding to another of the servobands (e.g., to compare with the servo information read by the first ofthe groups 962, 964), etc.

Looking now to FIG. 9H, the servo reader configuration 970 has groups972, 974 of servo readers, each of which includes three individual servoreaders 988, 990, 992 and 994, 996, 998 respectively. As shown, each ofthe groups of servo readers 962, 964 is positioned at an opposite end ofthe array 977 of data transducers 978 along the cross-track direction910. Moreover, a longitudinal axis of each of the groups 972, 974 ofservo readers is parallel to the longitudinal axis of the array 977 ofdata transducers 978. The array 977 of data transducers 978 may includedata readers and/or data writers. Moreover, depending on the desiredapproach, the array 977 of data transducers 978 may include 32individual data transducers, 64 individual data transducers, 128individual data transducers, etc., or any other desired number ofindividual data transducers. Moreover, one or more of the servo readersmay have a height (measured along the longitudinal axis of the magnetictape head) that is about 1.75 μm, but could be higher or lower dependingon the desired approach.

A distance D₂ (measured in the cross-track direction 910) between thecenter of each of the immediately adjacent servo readers 988, 990, 992and 994, 996, 998 in each of the respective groups 972, 974 may be lessthan or equal to one third, preferably less than or equal to one sixth,of a prespecified width W of the given servo band. A magnetic tape headhaving immediately adjacent servo readers which are separated by adistance D₂ which is less than or equal to one sixth of a prespecifiedwidth W of the given servo band is highly desirable as the servo readersare thereby able to read servo patterns with added granularity andachieve improved track following efficiency for various different types(e.g., generations) of magnetic tape. For example, referring momentarilyto FIGS. 12A-12C, a magnetic tape head having three servo readers whichare separated by a distance D₂ which is less than or equal to one sixthof a prespecified width W of the given servo band is positionablerelative to a magnetic tape such that all three servo readers are ableto read servo information from one or more servo patterns in the givenservo band simultaneously. Accordingly, some of the servo readerscoupled to the magnetic tape head may be redundant, thereby improvingresilience against degraded performance caused by servo reader error.For example, the servo readers in a first of the groups 972, 974 may beused to read servo information from the servo patterns in acorresponding servo band, while the other one of the groups 972, 974 mayremain inactive in a backup capacity, simultaneously read servoinformation from servo patterns corresponding to another of the servobands (e.g., to compare with the servo information read by the first ofthe groups 972, 974), etc.

It follows that a magnetic tape may have a hybrid servo bandconfiguration which includes servo patterns which each have a widthwhich is less than or equal to one third of a prespecified width of thegiven servo band. Moreover, a magnetic tape head may have two groups ofservo readers, each group having at least two individual servo readers.Each of the immediately adjacent servo readers in a group are separatedby a distance which is less than or equal to one third of a prespecifiedwidth of the given servo band, thereby allowing the magnetic tape headto be positionable relative to a magnetic tape such that two or more ofthe servo readers in a single group are able to read servo informationfrom one or more servo patterns in the given servo band simultaneously.The number and relative spacing between the servo patterns in thevarious approaches described above in FIGS. 9C-9F, as well as the numberand relative spacing between servo readers in the various approachesdescribed above in FIGS. 9G-9H allow for a corresponding magnetic tapehead and tape drive to achieve improved performance while also enablingbackward compatibility for various styles (e.g., generations) ofmagnetic tape. As a result, by implementing the foregoing approaches,the shortcomings experienced in conventional products are overcome.Accordingly, referring now to FIG. 10, a flowchart of a tape-driveimplemented method 1000 is shown according to one embodiment. The method1000 may be performed in accordance with the present invention in any ofthe environments depicted in FIGS. 1-7 and 9A-9H, among others, invarious embodiments. Of course, more or less operations than thosespecifically described in FIG. 10 may be included in method 1000, aswould be understood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 1000 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 1000 may be partially or entirely performed by acontroller, a processor, etc., or some other device having one or moreprocessors therein. The processor, e.g., processing circuit(s), chip(s),and/or module(s) implemented in hardware and/or software, and preferablyhaving at least one hardware component may be utilized in any device toperform one or more steps of the method 1000. Illustrative processorsinclude, but are not limited to, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), etc., combinations thereof, or any other suitablecomputing device known in the art. According to one illustrativeapproach, logic may be integrated with and/or executable by controller128 of tape drive 100 of FIG. 2, the logic being configured to performand one or more of the processes described below in correspondence withmethod 1000.

As shown in FIG. 10, operation 1002 of method 1000 includes determininga servo band configuration of servo bands on a magnetic tape. Aconfiguration of the servo bands on a magnetic tape may be determined ina number of different ways. In preferred approaches, the servo bandconfiguration may be determined from a format associated with themagnetic tape. As previously mentioned, the format of a magnetic tapemay be written in a header of the magnetic tape itself, stored in memorylocated in a tape cartridge along with the magnetic tape, be encoded ina barcode coupled to a tape cartridge in which the magnetic tape isstored, etc. The format of the magnetic tape may include the servo bandconfiguration itself. However, the format of the magnetic tape may befurther used to determine the actual servo band configuration, e.g., bylook up the servo band configuration from a lookup table.

In other approaches, the servo band configuration on a magnetic tape maybe determined by sweeping a servo reader over an anticipated location ofa servo band (e.g., near an outer lateral edge of the magnetic tape) andreading the servo patterns. Moreover, the servo information gatheredfrom the signals read may be used to determine the servo bandconfiguration of the servo bands on the magnetic tape. In still otherapproaches, the servo band configuration of servo bands on a magnetictape may be determined by visually inspecting the servo bands on themagnetic tape, or any other process which would be apparent to oneskilled in the art after reading the present description.

Furthermore, operation 1004 includes using servo readers on a magnetictape head to read one or more of the servo bands based on the determinedservo band configuration. Again, depending on the servo bandconfiguration and/or the arrangement of servo readers included on themagnetic tape head, reading one or more of the servo bands may include anumber of different sub-processes (e.g., as will be described in furtherdetail below with reference to FIGS. 11A-12C).

With continued reference to method 1000, operation 1006 includes usingthe servo information read from the one or more of the servo bands toposition the magnetic tape head relative to the magnetic tape. The servoinformation read from the one or more servo bands may be used todetermine positioning information of the magnetic tape head relative tothe magnetic tape. As a magnetic tape is passed over a magnetic tapehead, the relative position of the magnetic tape head with respect tothe magnetic tape orientation changes constantly. For example, tapeskew, lateral tape motion, TDS, etc., vary while reading from and/orwriting to magnetic tape. Moreover, the velocity at which the magnetictape is passed over the magnetic tape head varies as well. Accordingly,the servo information read from one or more of the servo bands may beused to determine tape skew, lateral tape motion, TDS, tape velocity,etc., which may in turn be used to improve performance by maintaining adesired position of the magnetic tape head relative to the magnetic tapewith significantly improved efficiency compared to conventionalproducts, e.g., as will be described in further detail below.

Depending on the servo band configuration determined in operation 1002,and/or the arrangement (e.g., number) of servo readers included on themagnetic tape head, the operations included in method 1000 may includevarious sub-processes given the particular approach, e.g., servo readerconfiguration corresponding to the magnetic tape head. Accordingly,FIGS. 11A-11C below are illustrated in accordance with approaches inwhich the magnetic tape head has two groups of servo readers, each grouphaving two individual servo readers. One of the groups of servo readersis positioned at each end of an array of data transducers positionedalong the magnetic tape head in the cross-track direction. Moreover,each of the servo readers in a group are separated by a distance D₁which is less than or equal to one third of a prespecified width W ofthe given servo band, thereby allowing the magnetic tape head to bepositionable relative to a magnetic tape such that both servo readersare able to read servo information from one or more servo patterns inthe given servo band simultaneously. Similarly, FIGS. 12A-12C below areillustrated in accordance with approaches in which the magnetic tapehead has two groups of servo readers, each group having three individualservo readers. One of the groups of servo readers is positioned at eachend of an array of data transducers positioned along the magnetic tapehead in the cross-track direction. Moreover, each of the immediatelyadjacent servo readers in a group are separated by a distance D₂ whichis less than or equal to one sixth of a prespecified width W of thegiven servo band, thereby allowing the magnetic tape head to bepositionable relative to a magnetic tape such that all three servoreaders are able to read servo information from one or more servopatterns in the given servo band simultaneously.

Looking to FIGS. 11A-11C, exemplary sub-processes of reading servoinformation and using the servo information to position the magnetictape head are illustrated in accordance with one approach in which themagnetic tape head includes two groups of servo readers, each groupincluding two individual servo readers (e.g., see FIG. 9G). Any one ormore of sub-processes may be used to perform operations 1004 and/or 1006of FIG. 10. Accordingly, each of the sub-processes included in FIGS.11A-11C are shown as being a part of operations 1004 and 1006,respectively. However, it should be noted that the sub-processes ofFIGS. 11A-11C are illustrated in accordance with one approach which isin no way intended to limit the invention.

Referring specifically to FIG. 11A, the sub-processes illustrated inFIG. 11A may be performed in response to determining in operation 1002that each of the servo bands on a magnetic tape has a configurationsimilar to that of the servo band configuration 930 depicted in FIG. 9Dabove. In other words, the sub-processes illustrated in FIG. 11A may beperformed in response to determining in operation 1002 that each of theservo bands on a magnetic tape has a configuration of a third type.Although in no way intended to limit the invention, a “configuration ofa third type” is intended to correspond to a servo band configurationwhich includes a HD servo pattern and a TBS pattern, the HD servopattern and the TBS pattern each having a width that is one third of theprespecified width of the given servo band. For example, referring backto FIG. 9D momentarily, the servo band configuration 930 illustratedtherein is of a third type.

With continued reference to FIG. 11A, sub-operation 1102 includesreading information from the TBS pattern with a first servo reader ofone of the groups of servo readers, while sub-operation 1104 includesreading information from the HD servo pattern with a second servo readerof the one of the groups of servo readers. Again, the magnetic tape headin the present approach includes two groups of servo readers, each groupincluding two individual servo readers. Thus information may be readfrom the TBS and HD patterns with the servo readers in either (or both)of the groups of servo readers simultaneously. Moreover, depending onthe orientation of the HD servo pattern with respect to the TBS pattern,the “first servo reader” may be the servo reader in a group that iscloser to a specified first end of the magnetic tape head along itslongitudinal axis, while the “second servo reader” may be the servoreader in a group that is farther from the specified first end of themagnetic tape head, or vice versa.

It should be noted that each of the servo readers in a group of servoreaders on a given magnetic tape head according to any of the approachesdescribed herein may be able to read HD servo patterns as well as TBSservo patterns in the sense that each of the servo readers may be ableto generate a readback signal which corresponds to the respective servopattern when passed thereover while operational (e.g., powered on).However, depending on which type of servo pattern a particular readbacksignal corresponds to (e.g., TBS or HD), circuitry electrically coupledto the magnetic tape head which the servo readers correspond to mayroute the readback signal to a combination of components (e.g., acircuit) which is able to decode the readback signal and producereadback information based on the type of servo pattern the readbacksignal originated from, e.g., refer back to FIGS. 6 and 7 above.

Moreover, the servo information derived from the servo patterns of aservo band may be further used by the magnetic tape head and/or variousother components. For instance, sub-operation 1106 includes determining(e.g., decoding, calculating, etc.) a lateral position of the magnetictape head relative to the magnetic tape using the information read fromthe TBS pattern, as well as the information read from the HD servopattern. Moreover, sub-operation 1108 includes determining (e.g.,decoding, calculating, etc.) a velocity of the magnetic tape using theinformation read from the TBS pattern, as well as the information readfrom the HD servo pattern. The lateral position of the magnetic tapehead and/or the velocity of the magnetic tape may be determined usingany process which would be apparent to one skilled in the art afterreading the present description.

The lateral position of the magnetic tape head relative to the magnetictape may be used to reposition the magnetic tape head such that the datatransducers on the magnetic tape head are desirably positioned over thedata tracks of the corresponding data band. Moreover, the velocity oftape may be used to determine how fast or slow the data tracks should bewritten to the magnetic tape in some approaches. Accordingly, thelateral position of the magnetic tape head relative to the magnetic tapeand the velocity of the magnetic tape may be used to desirably positionthe magnetic tape head relative to the magnetic tape.

Implementing the various processes described in FIG. 11A desirablyresults in the ability to determine track following information whilealso enabling backward compatibility which is highly desirable forremovable storage media such as magnetic tape as described herein.According to an illustrative example, which is in no way intended tolimit the invention, various ones of the processes included in FIG. 11Amay be implemented in order to read a servo pattern such as thatillustrated in FIG. 8A above. In sharp contrast, conventional productshave relied on different tape drives for reading and/or writing tomagnetic tapes having different forms which results in decreased dataprocessing efficiency, decreased system resource utilization efficiency,etc.

Now looking to FIG. 11B, the sub-processes illustrated in FIG. 11B maybe performed in response to determining in operation 1002 that each ofthe servo bands on a magnetic tape has a configuration similar to thatof the servo band configuration 920 depicted in FIG. 9C above. In otherwords, the sub-processes illustrated in FIG. 11B may be performed inresponse to determining in operation 1002 that each of the servo bandson a magnetic tape has a configuration of a second type. Although in noway intended to limit the invention, a “configuration of a second type”is intended to correspond to a servo band configuration which includestwo TBS patterns and a HD servo pattern sandwiched between the two TBSpatterns. Moreover, each of the TBS patterns and the HD servo patterneach have a width that is one third of the prespecified width of thegiven servo band. For example, referring back to FIG. 9C momentarily,the servo band configuration 920 illustrated therein is of a secondtype.

With continued reference to FIG. 11B, decision 1120 includes determiningwhether the magnetic tape is traveling in a forward direction. Accordingto the present description, “in a forward direction” is intended torepresent the instance where the magnetic tape is being transitionedfrom supply reel (e.g., in a tape cartridge) to take-up reel (e.g., in atape drive). For instance, referring momentarily back to FIG. 2, it maybe determined that the magnetic tape 122 is traveling in a forwarddirection while being transitioned from supply cartridge 120 to take-upreel 121. In other words, a tape may be traveling in a forward directionwhen the magnetic tape is being passed over a magnetic head from thebeginning of tape and traveling towards the end of tape. Similarly, itmay be determined that the magnetic tape 122 is not traveling in aforward direction (but rather a backward direction) while beingtransitioned from take-up reel 121 to supply cartridge 120. However, itshould be noted that in other embodiments, “in a forward direction” mayrepresent instance where the magnetic tape is being transitioned fromtake-up reel to supply reel.

Referring back to FIG. 11B, the flowchart is shown as proceeding tosub-operation 1122 in response to determining that the magnetic tape istraveling in the forward direction. There, sub-operation 1122 includesreading information from a first of the two TBS patterns (e.g., see 924of FIG. 9C) with a first servo reader of one of the groups of servoreaders (e.g., see 986 of FIG. 9G). Moreover, sub-operation 1124includes reading information from the HD servo pattern (e.g., see 922 ofFIG. 9C) with a second servo reader of the one of the groups of servoreaders (e.g., see 984 of FIG. 9G). The flowchart also proceeds tosub-operation 1126 in response to determining that the magnetic tape isnot traveling in the forward direction. There, sub-operation 1126includes reading information from a second of the two TBS patterns(e.g., see 926 of FIG. 9C) with the second servo reader of the one ofthe groups of servo readers. Furthermore, sub-operation 1128 includesreading information from the HD servo pattern (e.g., see 922 of FIG. 9C)with the first servo reader of the one of the groups of servo readers.

It follows that servo information may preferably be read from a certainservo pattern with a certain servo reader depending on the direction inwhich the magnetic tape is traveling. For instance, referringmomentarily back to FIGS. 9C and 9G, according to an in-use example,which is in no way intended to limit the invention, while the magnetictape is traveling in a forward direction, a first (e.g., lower) one ofthe servo readers 986 in the first (e.g., lower) group of servo readers964 may be used to read the first (e.g., lower) TBS servo pattern 924while the second (e.g., upper) one of the servo readers 984 in the first(e.g., lower) group of servo readers 964 is used to read the HD servopattern 922. However, when the magnetic tape is traveling in a directionopposite from the forward direction, the second (e.g., upper) servoreader 984 in the first (e.g., lower) group of servo readers 964 may beused to read the second (e.g., upper) TBS pattern 926 while the first(e.g., lower) servo reader 986 in the first (e.g., lower) group of servoreaders 964 is used to read the HD servo pattern 922. Again, this in-useexample is presented for exemplary purposes only, and is in no wayintended to limit the invention. Moreover, the terms “upper” and “lower”are relative terms which are in used to merely represent a relativepositioning of the servo patterns and/or servo readers relative to eachother according to the in-use example. Thus, depending on theorientation of the magnetic tape head, the magnetic tape, the servoreaders, servo patterns, etc., the servo readers and/or servo patternsmay correspond differently.

Referring again to FIG. 11B, the flowchart proceeds to sub-operations1130 which includes determining (e.g., decoding) a lateral position ofthe magnetic tape head relative to the magnetic tape using theinformation read from the first or second of the two TBS patterns(depending on the direction of tape travel), as well as the informationread from the HD servo pattern. Furthermore, sub-operation 1132 includesdetermining (e.g., decoding) a velocity of the magnetic tape using theinformation read from the first or second of the two TBS patterns, aswell as the information read from the HD servo pattern. Again, themagnetic tape head in the present approach includes two groups of servoreaders, each group including two individual servo readers. Thusinformation may be read from the TBS and HD patterns with the servoreaders in either (or both) of the groups of servo readers. Moreover,the lateral position of the magnetic tape head and/or the velocity ofthe magnetic tape may be determined using any process which would beapparent to one skilled in the art after reading the presentdescription.

Implementing the various processes described in FIG. 11B desirablyresults in the ability to determine track following information whilealso enabling backward compatibility which is highly desirable forremovable storage media such as magnetic tape as described herein. Insharp contrast, conventional products have relied on different tapedrives for reading and/or writing to magnetic tapes having differentforms which results in decreased data processing efficiency, decreasedsystem resource utilization efficiency, etc.

Moving to FIG. 11C, the sub-processes illustrated in FIG. 11C may beperformed in response to determining in operation 1002 that each of theservo bands on a magnetic tape have a configuration similar to that ofthe TBS pattern 802 of FIGS. 8A-8B above. In other words, sub-processesillustrated in FIG. 11C may be performed in response to determining inoperation 1002 that each of the servo bands on a magnetic tape have aconfiguration of a first type. Although in no way intended to limit theinvention, a “configuration of a first type” is intended to correspondto a servo band configuration which includes a single TBS pattern havinga width that is two third of the prespecified width of the given servoband. For example, referring back to FIGS. 8A-8B momentarily, the TBSpattern 802 illustrated therein is of a first type.

With continued reference to FIG. 11C, sub-operation 1140 includesreading information from the TBS pattern with a first servo reader ofone of the groups of servo readers. Moreover, decision 1142 includesdetermining whether a second servo reader of the one of the groups ofservo readers is currently oriented over the TBS pattern. In otherwords, decision 1142 determines whether both of the servo readers in oneof the groups are oriented over the TBS pattern in a servo band.

The flowchart proceeds to sub-operation 1144 in response to determiningthat the second servo reader of the one of the groups of servo readersis not currently oriented over the TBS pattern. There, sub-operation1144 includes determining (e.g., decoding) a lateral position of themagnetic tape head relative to the magnetic tape using the informationread from the TBS pattern by the first servo reader. Moreover,sub-operation 1146 includes determining (e.g., decoding) a velocity ofthe magnetic tape using the information read from the TBS pattern by thefirst servo reader. The lateral position of the magnetic tape headand/or the velocity of the magnetic tape may be determined using anyprocess which would be apparent to one skilled in the art after readingthe present description.

Returning to decision 1142, the flowchart may proceed to sub-operation1148 in response to determining that the second servo reader of the oneof the groups of servo readers is currently oriented over the TBSpattern. There sub-operation 1148 includes reading information from theTBS pattern with the second servo reader of the one of the groups ofservo readers.

The flowchart of FIG. 11C further proceeds to sub-operation 1150 whichincludes determining (e.g., decoding) a lateral position of the magnetictape head relative to the magnetic tape using the information read fromthe TBS pattern by the second servo reader of the one of the groups ofservo readers, in addition to using the information read from the TBSpattern by the first servo reader of the one of the groups of servoreaders. Moreover, sub-operation 1152 includes determining (e.g.,decoding) a velocity of the magnetic tape using the information readfrom the TBS pattern by the second servo reader of the one of the groupsof servo readers, as well as the information read from the TBS patternby the first servo reader of the one of the groups of servo readers. Thelateral position of the magnetic tape head and/or the velocity of themagnetic tape may be determined in sub-operations 1150, 1152 using anyprocess which would be apparent to one skilled in the art after readingthe present description. It should also be noted that although a singlelateral position is determined in sub-operation 1150 using theinformation read from the TBS pattern by the second servo reader as wellas from the TBS pattern by the first servo reader, in other approaches alateral position may be determined from the information read from theTBS pattern by the second servo reader while another lateral positionmay be determined from the information read from the TBS pattern by thefirst servo reader, e.g., which may be averaged together. Similarly,although a single tape velocity is determined in sub-operation 1152using the information read from the TBS pattern by the second servoreader as well as from the TBS pattern by the first servo reader, inother approaches a tape velocity may be determined from the informationread from the TBS pattern by the second servo reader while another tapevelocity may be determined from the information read from the TBSpattern by the first servo reader, e.g., which may be averaged together.

Further still, sub-operation 1154 includes determining (e.g., compute) askew of the magnetic tape head relative to the magnetic tape, andsub-operation 1156 includes determining (e.g., compute) TDS informationcorresponding to the magnetic tape. As previously mentioned, accordingto an exemplary approach, the skew of the magnetic tape head may bedetermined using the servo information read by the servo readers in asame group. Accordingly, when two or more servo readers are able to readthe same TBS pattern at one end of the magnetic tape head, the skewbetween the relative orientation of the magnetic tape head and magnetictape may be determined, e.g., as described below with reference to FIGS.13A-13D. For instance, Equation 1 and/or Equation 2 may be used todetermine the skew of the magnetic tape head. This resulting ability ishighly desirable, as single servo band detection with multiple servoreaders on a single magnetic tape head allows skew and/or TDSmeasurements to be determined even while other servo band information isinvalid or unobtainable. Furthermore, this improved functionality isachieved while also enabling backward compatibility which is highlydesirable for removable storage media such as magnetic tape as describedherein. In sharp contrast, conventional products have determined tapeskew and TDS measurements from information gathered from servo bands onboth sides of a head module, or information from servo readers onmultiple head modules. In other words, to compute skew and/or TDS,conventional products have needed to obtain valid servo information frommore than one servo band and/or more than one head module. This makessuch conventional head modules particularly susceptible to degradedperformance and/or being rendered completely useless by servo defects,scratches caused by asperities on the surface of the magnetic tape, etc.

As a result, implementing a magnetic tape head which is able to performone or more of the various processes described in FIGS. 10-11C desirablyimproves tape drive performance, reduces readback error, etc.

According to some approaches, skew may be determined by using any of theprocesses described below with reference to FIGS. 13A-13D. As mentionedearlier, Equation 1 and/or Equation 2 may be used to determine the skewof the magnetic tape head. However, referring again to FIG. 11C, theskew of the magnetic tape head and/or the TDS information correspondingto the magnetic tape may be determined in sub-operations 1154, 1156using any process which would be apparent to one skilled in the artafter reading the present description.

The skew of the magnetic tape head relative to the magnetic tape may beused to reposition (e.g., rotate) the magnetic tape head such that thedata transducers on the magnetic tape head are desirably positionedrelative to the data tracks of the corresponding data band. Moreover,the TDS information corresponding to the magnetic tape may be used toreposition (e.g., laterally adjust) the magnetic tape head relative tothe magnetic tape in some approaches. Accordingly, the skew of themagnetic tape head relative to the magnetic tape and the TDS informationcorresponding to the magnetic tape may be used to desirably position themagnetic tape head relative to the magnetic tape.

Looking now to FIGS. 12A-12C, exemplary sub-processes of reading servoinformation and using the servo information to position the magnetictape head are illustrated in accordance with one approach in which themagnetic tape head includes two groups of servo readers, each groupincluding three individual servo readers (e.g., see FIG. 9H). Any one ormore of sub-processes may be used to perform operations 1004 and/or 1006of FIG. 10. However, it should be noted that the sub-processes of FIGS.12A-12C are illustrated in accordance with one approach which is in noway intended to limit the invention.

Referring specifically to FIG. 12A, the sub-processes illustrated inFIG. 12A may be performed in response to determining in operation 1002that each of the servo bands on a magnetic tape has a configurationsimilar to that of the servo band configuration 950 depicted in FIG. 9Fabove. In other words, the sub-processes illustrated in FIG. 12A may beperformed in response to determining in operation 1002 that each of theservo bands on a magnetic tape has a configuration of a fifth type.Although in no way intended to limit the invention, a “configuration ofa fifth type” is intended to correspond to a servo band configurationwhich includes a HD servo pattern and a TBS pattern, the HD servopattern and the TBS pattern each having a width that is one sixth of theprespecified width of the given servo band.

With continued reference to FIG. 12A, sub-operation 1202 includesreading information from the TBS pattern with a first servo reader ofone of the groups of servo readers, while sub-operation 1204 includesreading information from the HD servo pattern with a second servo readerof the one of the groups of servo readers. Again, the magnetic tape headin the present approach includes two groups of servo readers, each groupincluding three individual servo readers. Thus information may be readfrom the TBS and HD patterns with the servo readers in either (or both)of the groups of servo readers simultaneously. Moreover, depending onthe orientation of the HD servo pattern with respect to the TBS pattern,the “first servo reader” may be the servo reader in a group that iscloser to a specified first end of the magnetic tape head along itslongitudinal axis, while the “second servo reader” may be the servoreader in a group that is farther from the specified first end of themagnetic tape head, or vice versa. Furthermore, the “first servo reader”may be the middle servo reader in the group, while the “second servoreader” may be one of the outer servo readers in that group, e.g.,depending on the approach.

Moreover, it should again be noted that each of the servo readers in agroup of servo readers on a given magnetic tape head according to any ofthe approaches described herein may be able to read HD servo patterns aswell as TBS servo patterns in the sense that each of the servo readersmay be able to generate a readback signal which corresponds to therespective servo pattern when passed thereover while operational (e.g.,powered on). However, depending on which type of servo pattern aparticular readback signal corresponds to (e.g., TBS or HD), circuitryelectrically coupled to the magnetic tape head and the servo readerscorresponding thereto may route the readback signal to a combination ofcomponents (e.g., a circuit) which is able to decode the readback signaland produce readback information based on the type of servo pattern thereadback signal originated from, e.g., refer back to FIGS. 6 and 7above.

Moreover, the servo information derived from the servo patterns of aservo band may be further used by the magnetic tape head and/or variousother components. For instance, sub-operation 1206 includes determining(e.g., decoding, calculating, etc.) a lateral position of the magnetictape head relative to the magnetic tape using the information read fromthe TBS pattern, as well as the information read from the HD servopattern. Moreover, sub-operation 1208 includes determining (e.g.,decoding, calculating, etc.) a velocity of the magnetic tape using theinformation read from the TBS pattern, as well as the information readfrom the HD servo pattern. The lateral position of the magnetic tapehead and/or the velocity of the magnetic tape may be determined usingany process which would be apparent to one skilled in the art afterreading the present description. The lateral position and/or velocity oftape may be used according to any desired approach.

Implementing the various processes described in FIG. 12A desirablyresults in the ability to determine track following information whilealso enabling backward compatibility which is highly desirable forremovable storage media such as magnetic tape as described herein. Insharp contrast, conventional products have relied on different tapedrives for reading and/or writing to magnetic tapes having differentforms which results in decreased data processing efficiency, decreasedsystem resource utilization efficiency, etc.

Now looking to FIG. 12B, the sub-processes illustrated in FIG. 12B maybe performed in response to determining in operation 1002 that each ofthe servo bands on a magnetic tape have a configuration similar to thatof the servo band configuration 940 depicted in FIG. 9E above. In otherwords, the sub-processes illustrated in FIG. 12B may be performed inresponse to determining in operation 1002 that each of the servo bandson a magnetic tape has a configuration of a fourth type. Although in noway intended to limit the invention, a “configuration of a fourth type”is intended to correspond to a servo band configuration which includestwo TBS patterns and a HD servo pattern sandwiched between the two TBSpatterns. Moreover, each of the TBS patterns and the HD servo patterneach have a width that is one sixth of the prespecified width of thegiven servo band.

With continued reference to FIG. 12B, decision 1220 includes determiningwhether the magnetic tape is traveling in a forward direction. Asdescribed above, “in a forward direction” is intended to represent theinstance where the magnetic tape is being transitioned from supply reel(e.g., in a tape cartridge) to take-up reel (e.g., in a tape drive). Forinstance, referring momentarily back to FIG. 2, it may be determinedthat the magnetic tape 122 is traveling in a forward direction whilebeing transitioned from supply cartridge 120 to take-up reel 121. Inother words, a tape may be traveling in a forward direction when themagnetic tape is being passed over a magnetic head from the beginning oftape and traveling towards the end of tape. Similarly, it may bedetermined that the magnetic tape 122 is not traveling in a forwarddirection (but rather a backward direction) while being transitionedfrom take-up reel 121 to supply cartridge 120. However, it should benoted that in other embodiments, “in a forward direction” may representinstance where the magnetic tape is being transitioned from take-up reelto supply reel.

Referring back to FIG. 12B, the flowchart is shown as proceeding tosub-operation 1222 in response to determining that the magnetic tape istraveling in the backward direction. There, sub-operation 1222 includesreading information from a first of the two TBS patterns with a firstservo reader of one of the groups of servo readers. Moreover,sub-operation 1224 includes reading information from the HD servopattern with a second servo reader of the one of the groups of servoreaders.

The flowchart also proceeds to sub-operation 1226 in response todetermining that the magnetic tape is traveling in the forwarddirection. There, sub-operation 1226 includes reading information from asecond of the two TBS patterns with the second servo reader of the oneof the groups of servo readers (e.g., see 998 of FIG. 9H). Furthermore,sub-operation 1228 includes reading information from the HD servopattern with the first servo reader of the one of the groups of servoreaders (e.g., see 996 of FIG. 9H), while sub-operation 1230 includesreading information from the first of the two TBS patterns with thethird servo reader positioned adjacent to the one of the groups of servoreaders (e.g., see 994 of FIG. 9H).

It follows that servo information may preferably be read from a certainservo pattern with a certain servo reader depending on the direction inwhich the magnetic tape is traveling. For instance, referringmomentarily back to FIGS. 9E and 9H, according to an in-use example,which is in no way intended to limit the invention, while the magnetictape is traveling in a forward direction, a first (e.g., middle) one ofthe servo readers 996 in the first (e.g., lower) group of servo readers974 may be used to read the HD pattern 942 while the second (e.g.,lowest) one of the servo readers 998 in the first (e.g., lower) group ofservo readers 974 is used to read the second (e.g., lowest) TBS servopattern 944 and the third (e.g., uppermost) servo reader 994 in thefirst (e.g., lower) group of servo readers 974 may be used to read thefirst (e.g., upper) TBS pattern 946. However, when the magnetic tape istraveling in a direction opposite the forward direction, the second(e.g., lowest) one of the servo readers 998 in the first (e.g., lower)group of servo readers 974 is used to read the HD servo pattern 942while the first (e.g., middle) servo reader 996 in the first (e.g.,lower) group of servo readers 974 is used to read the first (e.g.,upper) TBS servo pattern 946. Again, this in-use example is presentedfor exemplary purposes only, and is in no way intended to limit theinvention. Moreover, the terms “uppermost”, “middle” and “lowest” arerelative terms which are in used to merely represent a relativepositioning of the servo patterns and/or servo readers relative to eachother according to the in-use example. Thus, depending on theorientation of the magnetic tape head, the magnetic tape, the servoreaders, servo patterns, etc., the servo readers and/or servo patternsmay correspond differently.

Referring again to FIG. 12B, from sub-operation 1224 the flowchartproceeds to sub-operation 1232 which includes determining (e.g.,decoding) a lateral position of the magnetic tape head relative to themagnetic tape using the information read from the first of the two TBSpatterns by the first servo reader, as well as the information read fromthe HD servo pattern. Moreover, sub-operation 1234 includes determining(e.g., decoding) a velocity of the magnetic tape using the informationread from the first of the two TBS patterns by the first servo reader,as well as the information read from the HD servo pattern.

The flowchart is also shown as proceeding from sub-operation 1230 tosub-operation 1236 which includes determining (e.g., decoding) a lateralposition of the magnetic tape head relative to the magnetic tape usingthe information read from the second of the two TBS patterns by thesecond servo reader, and the information read from the HD servo patternby the first servo reader. Moreover, sub-operation 1238 includesdetermining (e.g., decoding) a velocity of the magnetic tape using theinformation read from the second of the two TBS patterns by the secondservo reader, and the information read from the HD servo pattern by thefirst servo reader.

Additionally, a lateral position of the magnetic tape head relative tothe magnetic tape as well as a tape velocity are determined from theservo information read from the information read from the first of thetwo TBS patterns. Accordingly, sub-operation 1240 includes determining(e.g., decoding) a lateral position of the magnetic tape head relativeto the magnetic tape using the information read from the first of thetwo TBS patterns by the third servo reader. Moreover, sub-operation 1242includes determining (e.g., decoding) a velocity of the magnetic tapeusing the information read from the first of the two TBS patterns by thethird servo reader.

Further still, sub-operation 1244 includes determining (e.g., compute) askew of the magnetic tape head relative to the magnetic tape, andsub-operation 1246 includes determining (e.g., compute) TDS informationcorresponding to the magnetic tape. Again, according to an exemplaryapproach, the skew of the magnetic tape head may be determined using theservo information read by the servo readers in a same group.Accordingly, when two or more servo readers are able to read tworespective TBS patterns at one end of the magnetic tape head, the skewbetween the relative orientation of the magnetic tape head and magnetictape may be determined. This resulting ability is highly desirable, assingle servo band detection with multiple servo readers on a singlemagnetic tape head allows skew and/or TDS measurements to be determinedeven while other servo band information is invalid or unobtainable.Moreover, this improvement is further exemplified when contrasted toconventional products which must check the timing to detect identifierfrom two different servo patterns on two different servo bands to assureskew information is decoded from same servo frame. As a result,implementing a magnetic tape head which is able to perform one or moreof the various processes described in FIGS. 10-12B desirably improvestape drive performance, reduces readback error, etc.

According to some approaches, the skew of the magnetic tape head may bedetermined using any of the processes described below with reference toFIGS. 14A-14D. For example, Equation 3 and/or Equation 4 may be used todetermine the skew of the magnetic tape head. However, referring againto FIG. 12B, the skew of the magnetic tape head and/or the TDSinformation corresponding to the magnetic tape may be determined insub-operations 1244, 1246 using any process which would be apparent toone skilled in the art after reading the present description.

Again, the skew of the magnetic tape head relative to the magnetic tapemay be used to reposition (e.g., rotate) the magnetic tape head suchthat the data transducers on the magnetic tape head are desirablypositioned relative to the data tracks of the corresponding data band.Moreover, the TDS information corresponding to the magnetic tape may beused to reposition (e.g., laterally shift) the magnetic tape headrelative to the magnetic tape in some approaches. Accordingly, the skewof the magnetic tape head relative to the magnetic tape and the TDSinformation corresponding to the magnetic tape may be used to desirablyposition the magnetic tape head relative to the magnetic tape.

Implementing the various processes described in FIG. 12B desirablyresults in the ability to determine the relative skew of the magnetictape and TDS while at least two servo readers are located above (able toread) a TBS pattern. This significantly reduces the frequency of readerrors, reduces magnetic tape head degradation, improves trackfollowing, etc., particularly in comparison to conventional products.Furthermore, this improved functionality is achieved while also enablingbackward compatibility which is highly desirable for removable storagemedia such as magnetic tape as described herein. In sharp contrast,conventional products have determined tape skew and TDS measurementsfrom information gathered from servo bands on both sides of a headmodule, or information from servo readers on multiple head modules. Inother words, to compute skew and/or TDS, conventional products haveneeded to obtain valid servo information from more than one servo bandand/or more than one head module. This makes such conventional headmodules particularly susceptible to degraded performance and/or beingrendered completely useless by servo defects, scratches caused byasperities on the surface of the magnetic tape, etc.

Moving to FIG. 12C, the sub-processes illustrated in FIG. 12C may beperformed in response to determining in operation 1002 that each of theservo bands on a magnetic tape has a configuration similar to that ofthe servo band configuration 930 depicted in FIG. 9D above. In otherwords, the sub-processes illustrated in FIG. 11A may be performed inresponse to determining in operation 1002 that each of the servo bandson a magnetic tape has a configuration of a third type. Although in noway intended to limit the invention, a “configuration of a third type”is intended to correspond to a servo band configuration which includes aHD servo pattern and a TBS pattern, the HD servo pattern and the TBSpattern each having a width that is one third of the prespecified widthof the given servo band. For example, referring back to FIG. 9Dmomentarily, the servo band configuration 930 illustrated therein is ofa third type.

With continued reference to FIG. 12C, sub-operation 1250 includesreading information from the TBS pattern with a second servo reader ofone of the groups of servo readers, while sub-operation 1252 includesreading information from the HD servo pattern with a third servo readerof the one of the groups of servo readers. Furthermore, decision 1254includes determining whether the second servo reader positioned adjacentto the one of the groups of servo readers is also currently orientedover the bottom half of the TBS pattern. As mentioned above, themagnetic tape head in the present approach includes two groups of servoreaders, each group including three individual servo readers (e.g., seeFIG. 9H). Accordingly, in some instances all three of the servo readersmay be positioned over servo patterns in a given servo band.

In response to determining that the second servo reader positionedadjacent to the one of the groups of servo readers is not also currentlyoriented over the bottom half of the TBS pattern, the flowchart proceedsto sub-operation 1256. There, sub-operation 1256 includes determining(e.g., decoding) a lateral position of the magnetic tape head relativeto the magnetic tape using the information read from the TBS pattern bythe second servo reader, and the information read from the HD servopattern by the first servo reader. Furthermore, sub-operation 1258includes determining (e.g., decoding) a velocity of the magnetic tapeusing the information read from the TBS pattern by the second servoreader, and the information read from the HD servo pattern by the firstservo reader.

However, returning to decision 1254, the flowchart proceeds tosub-operation 1260 in response to determining that the first servoreader positioned adjacent to the one of the groups of servo readers isalso currently oriented over the TBS pattern. There, sub-operation 1260includes reading information from the TBS pattern with the first servoreader as well.

Sub-operation 1262 further includes determining (e.g., decoding) alateral position of the magnetic tape head relative to the magnetic tapeusing the information read from the TBS pattern by the second servoreader, and the information read from the HD servo pattern by the thirdservo reader, while sub-operation 1264 includes determining (e.g.,decoding) a velocity of the magnetic tape using the information readfrom the TBS pattern by the second servo reader and the information readfrom the HD servo pattern by the third servo reader. Furthermore,sub-operation 1266 includes determining (e.g., computing) a skew of themagnetic tape head relative to the magnetic tape, and sub-operation 1268includes determining (e.g., computing) TDS information corresponding tothe magnetic tape.

According to an exemplary approach, the skew of the magnetic tape headmay be determined using any of the processes described below withreference to FIGS. 14A-14D. For example, Equation 3 and/or Equation 4may be used to determine the skew of the magnetic tape head. However,referring again to FIG. 12B, the skew of the magnetic tape head and/orthe TDS information corresponding to the magnetic tape may be determinedin sub-operations 1266, 1268 using any process which would be apparentto one skilled in the art after reading the present description.

Implementing the various processes described in FIG. 12C desirablyresults in the ability to determine the relative skew of the magnetictape and TDS while at least two servo readers are located above (able toread) a TBS pattern. This significantly reduces the frequency of readerrors, reduces magnetic tape head degradation, improves trackfollowing, etc., particularly in comparison to conventional products.Furthermore, this improved functionality is achieved while also enablingbackward compatibility which is highly desirable for removable storagemedia such as magnetic tape as described herein. In sharp contrast,conventional products have determined tape skew and TDS measurementsfrom information gathered from servo bands on both sides of a headmodule, or information from servo readers on multiple head modules. Inother words, to compute skew and/or TDS, conventional products haveneeded to obtain valid servo information from more than one servo bandand/or more than one head module. This makes such conventional headmodules particularly susceptible to degraded performance and/or beingrendered completely useless by servo defects, scratches caused byasperities on the surface of the magnetic tape, etc.

Looking now to FIGS. 13A-14D, exemplary processes for determining theskew of a magnetic head relative to a magnetic tape being passedthereacross are illustrated in accordance with different embodiments. Asan option, any of the present processes for determining the skew of amagnetic head relative to a magnetic tape being passed thereacross maybe implemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the otherFIGS., such as FIGS. 11C and 12C, e.g., as mentioned above.

Referring specifically to FIGS. 13A-13D, as shown in FIG. 13A and thedetailed view in FIG. 13B, the corresponding processes relate to aninstance in which two immediately adjacent servo readers 1300, 1301 arepositioned over (e.g., able to read) a same TBS pattern 1302. Themagnetic tape 1304 is preferably oriented such that the direction oftape travel is perpendicular to the longitudinal axis of the magnetictape head 1306. Therefore, looking to the relative angular orientationof the magnetic tape 1304 and magnetic tape head 1306, the magnetic tape1304 is skewed from an ideal orientation relative to the magnetic tapehead 1306 by an amount which is represented by angle θ. Moreover, theimmediately adjacent servo readers 1300, 1301 are separated by adistance D₃ which is measured in a direction along (parallel) thelongitudinal axis of the magnetic tape head 1306. The third servo reader1308 is also positioned over the HD servo pattern 1310 and preferablyreading servo information therefrom.

The graphs 1320, 1330 of FIGS. 13C-13D illustrate a servo correlatoroutput which corresponds to the readback signal received from the middleservo reader 1300 and the lower servo reader 1301, respectively. Thetiming offset τ₂−τ₁ represented in the plots of the graphs 1320, 1330results in part from the skew angle θ between the relative angularorientations of the magnetic tape head 1306 relative to the magnetictape 1304. Moreover, offsets Δ₁ and Δ₂ represent the amount of timingerror between the calculated (e.g., estimated) peak arrival time valueEstvalidFlag with the actual peak arrival time value seen in the plot onthe graph for each of the respective servo readers 1300, 1301.calculated (e.g., estimated) peak arrival time values EstvalidFlag maybe determined using known information about the synchronous servochannel in the tape drive being used to read the magnetic tape inaddition to the known (or knowable) velocity of tape, e.g., as would beappreciated by one skilled in the art after reading the presentdescription.

The following equations Equation 1 and Equation 2 represent theinterrelations of the relative orientations of the magnetic tape head1306 and the magnetic tape 1304. Accordingly, Equation 1 and/or Equation2 may be used to determine (e.g., calculate) skew related informationdepending on the desired approach as follows:φ=v(τ₂−τ₁+Δ₁−Δ₂)   Equation 1

where v is the velocity of the magnetic tape (e.g., tape speed).

$\begin{matrix}{{\tan\;\theta} = \frac{\varphi - {D_{3} \times \tan\;\alpha}}{D_{3}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where α is the azimuth angle of the servo bursts in the servo patterndepending on the type of magnetic tape (e.g., see Table 1 in relation toFIG. 4B above).

Similarly, looking now to FIGS. 14A-14D, as shown in FIG. 14A and thedetailed view in FIG. 14B, the corresponding processes relate to aninstance in which two immediately adjacent servo readers 1400, 1401 arepositioned over (e.g., able to read) two different TBS patterns 1402,1403. The magnetic tape 1404 is preferably oriented such that thedirection of tape travel is perpendicular to the longitudinal axis ofthe magnetic tape head 1406. Therefore, looking to the relative angularorientation of the magnetic tape 1404 and magnetic tape head 1406, themagnetic tape 1404 is skewed from an ideal orientation relative to themagnetic tape head 1406 by an amount which is represented by angle θ₂.Moreover, the immediately adjacent servo readers 1400, 1401 areseparated by a center-to-center distance D₄ which is measured in adirection along (parallel) the longitudinal axis of the magnetic tapehead 1406. The third servo reader 1408 is also positioned over the HDservo pattern 1410 and preferably reading servo information therefrom.

The graphs 1420, 1430 of FIGS. 14C-14D illustrate a servo correlatoroutput which corresponds to the readback signal received from the topservo reader 1400 and the lower servo reader 1401, respectively. Thetiming offset τ₄−τ₃ represented in the plots of the graphs 1420, 1430results in part from the skew angle θ2 between the relative angularorientations of the magnetic tape head 1406 relative to the magnetictape 1404. Moreover, Δ₃ and Δ₄ represent the amount of timing errorbetween the calculated (e.g., estimated) peak arrival time valueEstvalidFlag with the actual peak arrival time value seen in the plot onthe graph for each of the respective servo readers 1400, 1401.calculated (e.g., estimated) peak arrival time values EstvalidFlag maybe determined using known information about the synchronous servochannel in the tape drive being used to read the magnetic tape inaddition to the known (or knowable) velocity of tape, e.g., as would beappreciated by one skilled in the art after reading the presentdescription.

The following equations Equation 3 and Equation 4 represent theinterrelations of the relative orientations of the magnetic tape head1406 and the magnetic tape 1404. Accordingly, Equation 3 and/or Equation4 may be used to determine (e.g., calculate) skew related informationdepending on the desired approach as follows:φ=v ₂(τ₄−τ₃+Δ₃−Δ₄)   Equation 3

where v₂ is the velocity of the magnetic tape.

$\begin{matrix}{{\tan\;\theta} = \frac{\varphi}{D_{4}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Again, any of the processes for determining the skew of a magnetic headrelative to a magnetic tape being passed thereacross described inrelation to FIGS. 13A-14D may be implemented in conjunction withfeatures from any other embodiment listed herein, such as thosedescribed with reference to the other FIGS., such as FIGS. 11C and 12C.For instance, Equation 1 and/or Equation 2 may be used, at least inpart, to determine the skew of the magnetic tape head in sub-operation1154 of FIG. 11C. Moreover, Equation 3 and/or Equation 4 may be used, atleast in part, to determine the skew of the magnetic tape head insub-operation 1266 of FIG. 12C. Implementing one or more of theprocesses described in relation to FIGS. 13A-14D while determining theskew of the magnetic tape head, e.g., as seen in sub-operations 1154 and1266, is advantageous, as the accuracy of the resulting skew measurementis not decreased by timing offsets. As a result, adjustments made to thelateral and/or angular position of the magnetic tape head relative tothe magnetic tape may result in increased data read and/or writeefficiency.

As previously mentioned, the magnetic tape 902 illustrated in FIGS.9A-9F may be stored in a data storage cartridge. Looking now to FIG. 15,a data storage cartridge 1500 is illustrated in accordance with oneembodiment. As an option, the present data storage cartridge 1500 may beimplemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the other FIGS.However, such data storage cartridge 1500 and others presented hereinmay be used in various applications and/or in permutations which may ormay not be specifically described in the illustrative embodiments listedherein. Further, the data storage cartridge 1500 presented herein may beused in any desired environment. Thus FIG. 15 (and the other FIGS.) maybe deemed to include any possible permutation.

The data storage cartridge 1500 is shown as having an outer housing1502, which may include plastic(s), metal(s), rubber(s), etc., and/orcombinations thereof. The outer housing 1502 preferably defines an innerregion (which is obstructed from view) which is large enough to store amagnetic medium. Accordingly, the inner region of the data storagecartridge 1500 may include a magnetic tape. While the magnetic tape maybe stored in the data storage cartridge 1500 in any desired manner, itis preferred that the magnetic tape is wound on a flanged or flangelessspool which is in turn stored in the inner region of the data storagecartridge 1500.

The data storage cartridge 1500 also includes a cartridge memory 1504which is stored in the inner region of the data storage cartridge 1500and shown in a cutaway portion of the Figure, which is in no wayintended to limit the invention. It follows that certain informationcorresponding to the magnetic medium stored in the data storagecartridge 1500 may be saved in the cartridge memory 1504. For example, aformat in which a magnetic tape in the cartridge 1500 was produced maybe stored in the cartridge memory 1504. Thus, a prespecified width ofeach of the servo bands included in the magnetic tape may be determinedfrom the information stored in the cartridge memory 1504.

However, any configuration of data storage cartridge may be used whetheror not it includes the cartridge memory 1504. According to someapproaches, in place of or in addition to the cartridge memory 1504, thedata storage cartridge 1500 may include a barcode coupled to an outersurface of the outer housing 1502, a radio-frequency identification(RFID) tag coupled to the outer housing 1502, etc., and used to storeadditional information corresponding to a magnetic medium in the datastorage cartridge 1500.

Accordingly, various approaches described and/or suggested herein areable to successfully improve tape drive performance. As described above,it is preferred that magnetic tapes have a hybrid servo bandconfiguration which include servo patterns which each have a width whichis less than or equal to one third of a prespecified width of the givenservo band. Moreover, a magnetic tape head preferably includes twogroups of servo readers, each group having at least two individual servoreaders. Each of the immediately adjacent servo readers in a group areseparated by a distance which is less than or equal to one third of aprespecified width of the given servo band, thereby allowing themagnetic tape head to be positionable relative to a magnetic tape suchthat two or more of the servo readers in a single group are able to readservo information from one or more servo patterns in the given servoband simultaneously. It follows that the number and relative spacingbetween the servo patterns in the various approaches described herein,as well as the number and relative spacing between servo readers in thevarious approaches described herein allow for a corresponding magnetictape head and tape drive to achieve improved performance while alsoenabling backward compatibility for various styles (e.g., generations)of magnetic tape. As a result, by implementing the foregoing technicalfeatures, the shortcomings experienced in conventional products areovercome.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portableCD-ROM, a digital versatile disk (DVD), a memory stick, a floppy disk, amechanically encoded device such as punch-cards or raised structures ina groove having instructions recorded thereon, and any suitablecombination of the foregoing. A computer readable storage medium, asused herein, is not to be construed as being transitory signals per se,such as radio waves or other freely propagating electromagnetic waves,electromagnetic waves propagating through a waveguide or othertransmission media (e.g., light pulses passing through a fiber-opticcable), or electrical signals transmitted through a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), etc. By executable by the processor, what is meant is that thelogic is hardware logic; software logic such as firmware, part of anoperating system, part of an application program; etc., or somecombination of hardware and software logic that is accessible by theprocessor and configured to cause the processor to perform somefunctionality upon execution by the processor. Software logic may bestored on local and/or remote memory of any memory type, as known in theart. Any processor known in the art may be used, such as a softwareprocessor module and/or a hardware processor such as an ASIC, a FPGA, acentral processing unit (CPU), an integrated circuit (IC), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A tape drive-implemented method, comprising:using information read by one or more servo readers from one or moreservo bands on a magnetic tape to position a magnetic tape head relativeto the magnetic tape, wherein an array of data transducers is positionedalong the magnetic tape head, the array extending perpendicular to adirection of travel of the magnetic tape, wherein a group of servoreaders is positioned at each end of the array of data transducers,wherein a distance between each of the immediately adjacent servoreaders in each of the groups of servo readers is less than or equal toone third of a prespecified width of each of the servo bands, whereinthe distance between each of the servo readers in each of the groups andthe prespecified width are both measured in a direction perpendicular tothe direction of travel of the magnetic tape.
 2. A tape cartridge,comprising: a supply reel; and a magnetic tape having a plurality ofservo bands, wherein each of the servo bands includes a high densityservo pattern and two timing based servo patterns, wherein alongitudinal axis of each of the two timing based servo patterns isparallel to a longitudinal axis of the high density servo pattern,wherein a combined width of the high density servo pattern and one ofthe two timing based servo patterns in a given servo band is less thanor equal to two thirds of a prespecified width of each of the servobands, wherein the combined width and the prespecified width are eachmeasured in a direction perpendicular to a longitudinal axis of themagnetic tape.
 3. The tape cartridge as recited in claim 2, wherein awidth of each of the two timing based servo patterns and a width of thehigh density servo pattern are each less than or equal to one third ofthe prespecified width, wherein the width of each of the two timingbased servo patterns and the width of the high density servo pattern aremeasured in the direction perpendicular to the longitudinal axis of themagnetic tape.
 4. The tape cartridge as recited in claim 2, wherein awidth of each of the two timing based servo patterns and a width of thehigh density servo pattern are each less than or equal to one sixth ofthe prespecified width, wherein the width of each of the two timingbased servo patterns and the width of the high density servo pattern aremeasured in the direction perpendicular to the longitudinal axis of themagnetic tape.
 5. A computer program product for positioning a magnetichead, the computer program product comprising a computer readablestorage medium having program instructions embodied therewith, theprogram instructions executable by a tape drive to cause the tape driveto perform a method comprising: using, by the tape drive, informationread by one or more servo readers from one or more servo bands on amagnetic tape to position a magnetic tape head relative to the magnetictape, wherein an array of data transducers is positioned along themagnetic tape head, the array extending perpendicular to a direction oftravel of the magnetic tape, wherein a group of servo readers ispositioned at each end of the array of data transducers, wherein adistance between each of the immediately adjacent servo readers in eachof the groups of servo readers is less than or equal to one third of aprespecified width of each of the servo bands, wherein the distancebetween each of the servo readers in each of the groups and theprespecified width are both measured in a direction perpendicular to thedirection of travel of the magnetic tape.
 6. The computer programproduct as recited in claim 5, the program instructions executable bythe tape drive to cause the tape drive to perform the method comprising:determining, by the tape drive, a servo band configuration of the servobands on the magnetic tape, wherein in response to determining that eachof the servo bands is of a third configuration having a high densityservo pattern and a timing based servo pattern, the high density servopattern and the timing based servo pattern each having a width measuredin the direction perpendicular to the direction of travel of themagnetic tape, each of the widths being one third of the prespecifiedwidth: using the servo readers to read the one or more of the servobands includes: reading information from the timing based servo patternwith a first servo reader of one of the groups of servo readers; andreading information from the high density servo pattern with a secondservo reader of the one of the groups of servo readers.
 7. The computerprogram product as recited in claim 6, wherein using information readfrom one or more servo bands on a magnetic tape to position the magnetictape head relative to the magnetic tape includes: determining a lateralposition of the magnetic tape head relative to the magnetic tape using:the information read from the timing based servo pattern, and theinformation read from the high density servo pattern; and determining avelocity of the magnetic tape using: the information read from thetiming based servo pattern, and the information read from the highdensity servo pattern.
 8. The computer program product as recited inclaim 5, the program instructions executable by the tape drive to causethe tape drive to perform the method comprising: determining, by thetape drive, a servo band configuration of the servo bands on themagnetic tape, wherein in response to determining that each of the servobands is of a second configuration having two timing based servopatterns and a high density servo pattern sandwiched between the twotiming based servo patterns, each of the timing based servo patterns andthe high density servo pattern each having a width measured in thedirection perpendicular to the direction of travel of the magnetic tape,each of the widths being one third of the prespecified width: using theservo readers to read the one or more of the servo bands includes:determining whether the magnetic tape is traveling in a forwarddirection; reading information from a first of the two timing basedservo patterns with a first servo reader of one of the groups of servoreaders in response to determining that the magnetic tape is travelingin a forward direction; reading information from the high density servopattern with a second servo reader of the one of the groups of servoreaders in response to determining that the magnetic tape is travelingin a forward direction; reading information from a second of the twotiming based servo patterns with the second servo reader of the one ofthe groups of servo readers in response to determining that the magnetictape is not traveling in a forward direction; and reading informationfrom the high density servo pattern with the first servo reader of theone of the groups of servo readers in response to determining that themagnetic tape is not traveling in a forward direction.
 9. The computerprogram product as recited in claim 8, wherein using information readfrom one or more servo bands on a magnetic tape to position the magnetictape head relative to the magnetic tape includes: determining a lateralposition of the magnetic tape head relative to the magnetic tape using:the information read from the first or second of the two timing basedservo patterns, and the information read from the high density servopattern; and determining a velocity of the magnetic tape using: theinformation read from the first or second of the two timing based servopatterns, and the information read from the high density servo pattern.10. The computer program product as recited in claim 5, the programinstructions executable by the tape drive to cause the tape drive toperform the method comprising: determining, by the tape drive, a servoband configuration of the servo bands on the magnetic tape, wherein inresponse to determining that each of the servo bands are of a firstconfiguration having a timing based servo pattern with a width measuredin the direction perpendicular to the direction of travel of themagnetic tape, the width being two thirds of the prespecified width:using the servo readers to read the one or more of the servo bandsincludes: reading information from the timing based servo pattern with afirst servo reader of one of the groups of servo readers.
 11. Thecomputer program product as recited in claim 10, wherein usinginformation read from one or more servo bands on a magnetic tape toposition the magnetic tape head relative to the magnetic tape includes:determining, by the tape drive, a lateral position of the magnetic tapehead relative to the magnetic tape using: the information read from thetiming based servo pattern; and determining, by the tape drive, avelocity of the magnetic tape using: the information read from thetiming based servo pattern.
 12. The computer program product as recitedin claim 11, the program instructions executable by the tape drive tocause the tape drive to perform the method comprising: determining, bythe tape drive, whether a second servo reader of the one of the groupsof servo readers is oriented over the timing based servo pattern; and inresponse to determining that the second servo reader of the one of thegroups of servo readers is oriented over the timing based servo pattern:using the servo readers to read the one or more of the servo bandsincludes: reading information from the timing based servo pattern withthe second servo reader of the one of the groups of servo readers, andusing the information read from the one or more of the servo bands toposition the magnetic tape head relative to the magnetic tape includes:determining a lateral position of the magnetic tape head relative to themagnetic tape using: the information read from the timing based servopattern by the second servo reader of the one of the groups of servoreaders; determining a velocity of the magnetic tape using: theinformation read from the timing based servo pattern by the second servoreader of the one of the groups of servo readers; determining a skew ofthe magnetic tape head relative to the magnetic tape; and determiningtape dimensional stability information corresponding to the magnetictape.
 13. The computer program product as recited in claim 5, whereineach group of servo readers includes a third servo reader, wherein adistance between each of the servo readers and an immediately adjacentone of the servo readers in the respective group of servo readers isless than or equal to one sixth of a prespecified width of each of theservo bands.
 14. The computer program product as recited in claim 13,wherein in response to determining that each of the servo bands are of afifth configuration having a high density servo pattern and a timingbased servo pattern, the high density servo pattern and the timing basedservo pattern each having a width measured in the directionperpendicular to the direction of travel of the magnetic tape, each ofthe widths being one sixth of the prespecified width: using the servoreaders to read the one or more of the servo bands, wherein using theservo readers to read the one or more of the servo bands includes:reading information from the timing based servo pattern with a firstservo reader of one of the groups of servo readers; and readinginformation from the high density servo pattern with a second servoreader of the one of the groups of servo readers.
 15. The computerprogram product as recited in claim 14, wherein using the informationread from the one or more of the servo bands to position the magnetictape head relative to the magnetic tape includes: determining a lateralposition of the magnetic tape head relative to the magnetic tape using:the information read from the timing based servo pattern, and theinformation read from the high density servo pattern; and determining avelocity of the magnetic tape using: the information read from thetiming based servo pattern and the information read from the highdensity servo pattern.
 16. The computer program product as recited inclaim 13, wherein in response to determining that each of the servobands are of a fourth configuration having two timing based servopatterns and a high density servo pattern sandwiched between the twotiming based servo patterns, each of the timing based servo patterns andthe high density servo pattern each having a width measured in thedirection perpendicular to the direction of travel of the magnetic tape,each of the widths being one sixth of the prespecified width:determining whether the magnetic tape is traveling in a forwarddirection; in response to determining that the magnetic tape istraveling in a forward direction: using the servo readers to read theone or more of the servo bands, wherein using the servo readers to readthe one or more of the servo bands includes: reading information from afirst of the two timing based servo patterns with a first servo readerof one of the groups of servo readers; and reading information from thehigh density servo pattern with a second servo reader of the one of thegroups of servo readers, and using the information read from the one ormore of the servo bands to position the magnetic tape head relative tothe magnetic tape includes: determining a lateral position of themagnetic tape head relative to the magnetic tape using: the informationread from the first of the two timing based servo patterns, and theinformation read from the high density servo pattern; and determining avelocity of the magnetic tape using: the information read from the firstof the two timing based servo patterns, and the information read fromthe high density servo pattern.
 17. The computer program product asrecited in claim 16, wherein in response to determining that themagnetic tape is not traveling in a forward direction, using the servoreaders to read the one or more of the servo bands includes: readinginformation from a second of the two timing based servo patterns withthe second servo reader of the one of the groups of servo readers;reading information from the high density servo pattern with the firstservo reader of the one of the groups of servo readers; and readinginformation from the first of the two timing based servo patterns withthe third servo reader positioned adjacent to the one of the groups ofservo readers, and using the information read from the one or more ofthe servo bands to position the magnetic tape head relative to themagnetic tape includes: determining a lateral position of the magnetictape head relative to the magnetic tape using: the information read fromthe second of the two timing based servo patterns, and the informationread from the high density servo pattern; determining a velocity of themagnetic tape using: the information read from the second of the twotiming based servo patterns, and the information read from the highdensity servo pattern; determining a lateral position of the magnetictape head relative to the magnetic tape using: the information read fromthe first of the two timing based servo patterns; determining a velocityof the magnetic tape using: the information read from the first of thetwo timing based servo patterns; determining a skew of the magnetic tapehead relative to the magnetic tape; and determining tape dimensionalstability information corresponding to the magnetic tape.
 18. Thecomputer program product as recited in claim 13, wherein in response todetermining that each of the servo bands are of a third configurationhaving a high density servo pattern and a timing based servo pattern,the high density servo pattern and the timing based servo pattern eachhaving a width measured in the direction perpendicular to the directionof travel of the magnetic tape, each of the widths being one third ofthe prespecified width: using the servo readers to read the one or moreof the servo bands, wherein using the servo readers to read the one ormore of the servo bands includes: reading information from the timingbased servo pattern with a first servo reader of one of the groups ofservo readers; and reading information from the high density servopattern with a second servo reader of the one of the groups of servoreaders, and using the information read from the one or more of theservo bands to position the magnetic tape head relative to the magnetictape includes: determining a lateral position of the magnetic tape headrelative to the magnetic tape using: the information read from thetiming based servo pattern, and the information read from the highdensity servo pattern; and determining a velocity of the magnetic tapeusing: the information read from the timing based servo pattern, and theinformation read from the high density servo pattern.
 19. The computerprogram product as recited in claim 18, the program instructionsexecutable by the tape drive to cause the tape drive to perform themethod comprising: determining, by the tape drive, whether the thirdservo reader positioned adjacent to the one of the groups of servoreaders is oriented over the timing based servo pattern; in response todetermining that the third servo reader is oriented over the timingbased servo pattern: using the servo readers to read the one or more ofthe servo bands includes: reading information from the timing basedservo pattern with the third servo reader in response to determiningthat the third servo reader is oriented over the timing based servopattern, and using the information read from the one or more of theservo bands to position the magnetic tape head relative to the magnetictape includes: determining a lateral position of the magnetic tape headrelative to the magnetic tape using: the information read from thetiming based servo pattern by the third servo reader; determining avelocity of the magnetic tape using: the information read from thetiming based servo pattern by the third servo reader; determining a skewof the magnetic tape head relative to the magnetic tape; and determiningtape dimensional stability information corresponding to the magnetictape.
 20. The computer program product as recited in claim 5, whereinthe tape drive includes: a magnetic tape head; and a controller.